1854-1 91 5.

LATE X S V . )

~ ’ A U L EHILLILW was born at Strehlen, a small town in Silesia, in 1854. H e was of Jewish extraction, and was a cousin on his mother’s side of Cell Weigert. The two nien were intimate friends, and had much in coinnion ; both were speculators, and both were inventors of methods. Ehrlich received his early education at dtrehlen, and at the Gymnasium at Breslau. He spent also his first University semester in Breslau, studying scientific subjects, and then proceeded to Strassburg, where he decided to take up the study of medicine. Even at this early period there are evidences of his originality and independence of thought, and whatever influence he may have received from his teachers, there is little trace of i t in his subsequent work. It is recorded that when a student of medicine he became acquainted with, and was much impressed by, a paper of Heubel on lead poisoning, in wliich it was claimed that the organs where the lead accumulated during life had also in the dead condition the property of fixing the metal. He repealed Heubel’s observations, and, having difficulty with the estimation of lead in the organs, he conceived the idea of employing a colourecl substance to study the question of distribution and fixation, and for this purpose he used fuchsin with success. He attracted the attention of Waldeyer by his application of aniline dyes in histology, and received encourageinent from that distinguished anatomist to pursue his inquiries in this direction. With fixation and distribution as a principle of inquiry, derived initially. from Heubel, and with aniliiie dyes as a method of testing, Ehrlich may be said to have been eqnipped thns early for the first period of his re- searches. After completing his curriculum and passing the Staats- esaiiien, he wurli-ed for a year in the Pathological Institute under Cohn- heim and Heidenhain, and was then, in 1877, appointed Chief Assistant in Frerich’s Cliniqae in Berlin. Although the problems of clinical medicine appealed to him, its practical details were little to his taste. But the post gave him the opportunity to carry on researches on the manias , leuccemias, etc., which first brought his name into pro- miuence. He was, moreover, able to carry out investigation6 of a

JOURNAL OF PATHOLOGY.-VOL. XX. PLATE SX\J.

OBITUARI.: 35 1

more purely scientific nature, bearing on the chemical affinities of the living tissues.

The first period of Ehrlich’s scientific life, enibraciug about ten years, may be said to be chiefly occupied with the study of the com- bining affinities of chemical substances for the constituents of the tissues, especially as these can be revealed by staining reactions. At first this was carried out by means of film preparations, fixed by heat in order to avoid the possible disturbing effect of a chemical fixative. The method was not strictly histological, but micro-chemical ; it was a Parbenanalyse, and it was fruitful beyond anticipation. He discovered the mast -cells, and in his first paper described their specific granulations and their distribution in the tissue. Subsecluent papers dealt with the eosinophil and neutrophil cells, and he arrived a t the classification of the leucocytes according to their granulations or the absence of these-a classification which substantially remains to the present day. He distinguished leucze,mias according to their essential nature, showing that the ‘‘ splenic ” form really originated in the bone- marrow. He distinguished normoblasts and megaloblasts, and assigned their significance ; and he described polychromatophilia, and other changes in the red cells in disease.

Other interesting observations were made by him on aplastic anzemia and hzmoglobinuria. He insisted on the essential distinction between the lymphoid and myeloid tissues, and showed that leucocytosis was a function of the bone-marrow, thus establishing its importance as a tissue of defence. In short, he established nearly all the main facts of hzematology, and so laid the foundation for the study of the specific reactions of cells to various infections and stimuli, his work in this respect being complementary to that of Metchnikoff. In these earlier years he introduced many other new methods, which cannot be described in detail. We may, however, mention the methods for demonstrating glycogen in leucocytes and for estimating the alkalinity of the blood, the diazo reaction, and various bacterial and tissue stains. And it must not be omitted that he was the first to demonstrate the acid-fast character of the tubercle bacillus, and that he introduced the principle of staining which has been in universal application ever since.

His researches on staining, however, were not confined to dead cells and tissues. It was natural that he should inquire what, if any, affinity could be demonstrated between aniline dyes and the constituents of the living body. The result was theintroduction of the i?~t?.a &am method of staining. He found that for various reasons only a few dyes were suitable for the purpose, and of these methylene-blue gave the most remarkable results. When this dye was introduced into the circulation, or when the living organism was placed in it, the processes of certain nerve-cells, down to their finest endings, were stained blue. Pursuing further the question as to why only certain elements became stained, he believed that the essential conditions

352 PAUL ENRLICH;

were saturation with oxygen and an alkaline reaction. As is well known, the methylene-blue method has been extensively used and further developed by others, and has been of great service to zoologists and neurologists.

But perhaps the most important application of staining in the living tissue is contained in his ‘‘ Sauerstoffbedurfnis des Organismus,” published in 1885, a work characterised by a great ingenuity of methods and containing the germ of his side-chain theory. The work may be said to be a comparative study of the oxygen affinities of different tissues by means of two dyes, namely, alizarin-blue and indophenol, both of which are reducible to colourless forms or leuco-compounds. The former has a greater affinity for oxygen than the latter, and is thus less easily reduced, and accordingly, if in any particular circumstance a tissue reduces one but not the other, he supposed that its oxygen affinity must lie between that of the two dyes. Both are insoluble in water, but he introduced theni in such a way that they passed into a colloidal state in the blood. The method was to inject a certain quantity into the circulation of rabbits, to kill the animals after a suitable interval, and then to examine the con- dition of the organs. Some organs were found to be blue-they did not reduce the dye : some were colourless, and these were proved to contain the corresporiding leuco-compounds. Of the former some be- came colourless when respiration was stopped before death, owing to their reducing the dye in the absence of the normal oxygen supply. In this way Ehrlich gained an insight into the oxygen-affinities of different cells, and he supposed that just as the alkali-binding groups of phosphoric acid have different degrees of affinity for soda, and thus different calorimetric values, so the cells contain groups with varying avidity for oxygen: or, in other words, the cellular protoplasm in various organs has different side-chains whose function is to fix oxygen for the needs of the cells.

In 1886 Ehrlich found that he had contracted tubercle, apparently as the result of accidental infection in the course of his researches. I n consequence he gave up his work for a year and a half, which he spent in travelling abroad, and as a result of this, along with treat- ment by Koch’s tuberculin, a cure was happily efkected. Returning to Berlin, he worked €or EL time in a small private laboratory, and there- after obtained a post in the Institute for Infectious Disease, which he held for several years. When the new Serum Institute a t Steglitz was opened in 1896, Ehrlich was appointed Director, on the yecorn- mendation of Althoff, the Yrussian State Minister, a nian to whose eiilightennient and appreciative faculty he owed much. During this period, which terminated on his transference to Frankfurt, he carried on his long series of investigations on immunity, especially in connec- tion with antitoxins, and elaborated his side-chain theory. It may be recalled that antitoxins had been discovered in the case of tetanus by

OBITUAR Y. 353

Eehring and Kitasato in 1890, and apparently at this time Ehrlich was already engaged with researchee on ricin and abrin, his full results being published in the following year. He showed that specific immunity against each of these vegetable toxalbumens could be developed by feeding rabbits and mice for a certain period, and that in each case the serum had a specific antitoxic action on the corre- sponding toxin. Here again, as regards the nature of the poison used and the method of its introduction into the body, new ground was broken. Antitoxic action was thus not peculiar to the class of bacterial products: and it is quite possible that the development of antitoxin by feeding suggested the view afterwards developed that such toxins corresponded structurally with food-stuffs. Later, he showed that immunity against these poisons was transmissible to the offspring from the mother, but not from the father, and also that tihis was clue to a direct transference of antitoxin from the blood of the mother to that of the f e tus ; and later still, he found that the young animal might also acquire such immunity through the milk. In these cases immunity was shown to be of the passive or trans- ferred kind.

In view of Ehrlich’s previous work, i t was only natural that he should take up the subject of antitoxic action. From an early period of his researches on this subjecb, and a t a time when the contrary view was maintained by many, he was a strong advocate of the direct action of antitoxin ; and he ultimately proved that toxin and antitoxin united directly to form a substance neutral to the tissues ; though the independent researches of others in this connection must not be ignored. Specific combination and consequent neutralisation are the essential features of antitoxic action. His earlier researches, as we have seen, dealt with the distribution and fixation of chemical substances, but in the case of toxins there is of course another factor, namely, the poison- ing of the cells. His view as to the dual constitution of a toxin, represented by the haptophore and toxophore groups, seems to follow as a natural consequence, and i t has been amply supported by his subsequent researches. I n the action of toxin within the body there is, as in the case of other chemical substances, first of all fixation to the cells. This is an essential preliminary to toxic action. The anti- toxin with its specific combining group can hardly be regarded as a new formation, and seeing that as a rule none is present in the blood, it must be considered as normally a constituent of cells. Again, since certain groups in the cells-cell-receptors-can fix toxin, it is reasonable to suppose that it is these groups which become separated as antitoxin. Antitoxin molecules are thus the shed or cast-off receptors or side-chain8 of the cells. These steps in the theory seem to follow in logical sequence. But why are the molecules thus shed off? Ehrlich regarded the receptors as binders of food-stuffs in the process of nutrition. The toxins are taken up in disguise; they

354 PAUL EHRLICH.

masquerade as food-stuffs, but as they prove to be harniful, they are thrown off in union with the receptors. The receptors are regenerated, and then, the process Leing often repeated, they are regenerated in excess and appear free in the blood. Such is the early stage and essence of his side-chain theory. With the discovery of other anti- substances-precipitins, agglutins, and lysins-the theory was extended to include these also, bnt no new principle of importance was neces- sary. It would be out of place as it would be fruitless, to attempt a discussion of the side-chain theory. Many have been the criticisms of it, some in ignorance, some with justice, but through time only can its valne be tested. We have tried rather to trace the steps hy which i t was evolved, and to whatever extent it may be proved to hold good there is no doubt that it forms the guiding principle in many of Ehrlich’s researches, and was in his hands fruitful of practical results.

But apart from the analytical and theoretical aspect of the question, the value of Ehrlich’s work in this department is very great. He studied the phenomena of antitoxin production in the living body, and showed how the immunity curve corresponded with the view as to the direct combination of toxin and antitoxin : he revealed the variations of the toxin molecules, the formation of toxoids in vityo, and analysed their effect in the process of neutralisation by antitoxin. In the case of ricin, he showed that its antitoxin annulled its agglutinating action on the red corpuscles, thus demonstrating the direct effect without the interventioii of living cells ; he also showed that the union of toxin and antitoxin was regulated by temperature and by the degree of concentration. He revealed the production of multiple toxins by a bacterium-the tetanolysin in addition to the tetano-spasmin in tetanus-toxin, the toxone and its special action in the case of diph- theria toxin,-and these results shadowed forth the still greater multiplicity of toxins established afterwards in the case of snake venoms. The great practical outcome of painstaking labour, extending over many years, was the method of exact estimation of diphtheria antitoxin by a permanent standard, a method which has been in all but universal use down to the present day. His monograph dealing with this subject, ‘I Die Werthbestimmung des Diphtherieheilserums,” which was published in 1897, is a masterpiece in research and a monument of his remarkable powers of analysis and his thoroughness in working out details, even although certain of his interpretations may be open to challenge.

The discovery of hamolytic sera by Bordet in 1898 led to a brilliant series of researches by Ehrlich in association with Morgen- roth and others. These were begun in Berlin, and continued in Frankfurt when Ehrlich went there to take up his new duties. Exactitude in method and visibility of result had always appealecl to him, and these were attainable in test-tube hwnolytic experiments in a mariner never before possible. The outcome was a new analysis of

OBlTUA RZ.: 355

immunity phenomena, and a remarkable differentiation of bodies in the serum, by comparatively simple means. The researches 011

hcemolysis were numerous, and were published as a volume in 1904 -a work which is exceedingly suggestive and rich in results. The analysis of specificity is a contribution of permanent value, and amongst the views on which Ehrlich laid special stress are those on the amboceptor nature of immune-body and on the multiplicity of complements : as is well known, they have been the subject of much controversy. Some of his niodes of representation may appear to be of too mechanical a kind, but they must not be taken too literally, as he did not intend them to be. The leading ideas form a further development of the side-chain theory, but the work is of too detailed a nature to be presented even in summary. It will remain a store- house from which others may draw with profit.

It is not naturally related to his lines of research, and the subject was not one of his own choice, the investigations being undertaken by him by special request, as a fund of money had been left for the purpose. Nevertheless he devoted his energies to it with enthusiasm, and his masterly powers are shown in this as in previous researches. Ehrlich soon convinced himself that the parasitic origin of cancer was unten- able; to him the cancer-cell was a body cell altered in its habits, a cell which had increased avidity for nourishment as compared with the normal body cells. After much preliminary work, the first great step was to obtain tumours growing in such conditions as to make them easily accessible to experimental inquiry : to have, as it were, cultures of different strains growing in the animal body. This was carried out in the case of mice on a most extensive scale, and it is stated that upwards of a thousand different growths have since been studied by this method in the Frankfurt Institute. Though no outstanding practical result was obtained, and as to this Ehrlich himself was never sanguine, important advances wese made in our knowledge of the nature of tumour growth. It was shown that active immunity could be produced by methods analogous to those which obtain in bacteriology, the immunising agent being, however, always cells from the same species of animal, either normal cells or tnniour cells altered in certain ways. The varying effects of different degrees of immunity on histological structure is another important subject, and the development of sarconia under the influence of a growing carcinoma is now a widely recognised observation. It clearly appeared from the experimental results that proliferation of tumour cells is not all- powerful, as one might say, but that certaiu slight alterations in the environment are sufficient to stop it. Failure of growth thus became an important subject of inquiry, and, in connection with it, Ehrlich developed his theory of athrepsy and athreptic immunity. Athrepsy may be said to be a condition of non-assimilation, owing to a want of

Ehrlich’s experimental work on cancer was begun in 1901.

356 PA UL EHRLICH.

suitability or correspondence bet ween the cell-receptors and food molecules, or other substances in the environment. Tumour cells require a sufficiency of special nourishment which is peculiar to the species. A mouse tumour grows for a time in the tissue of the rat, and then ceases to grow ; the rat cannot supply the substance necessary to maintain growth, and the temporary growth is due to some of the necessary material being transferred originally from the mouse. The case is not one of active immunity on the part of the rat : it is one of athrepsy. So, also, the failure of metastases to grow in internal organs, when the primary tuinonr is large, Ehrlich ascribes to athrepsy. In this ease it was shown that metastases actually occurred, but failed to develop owing to a deficiency of the necessary nourishment, brought about by excessive consumptioil in the primary growth. Later, he applied the theory to other departments of pathology and also to therapy. Just as the influenza bacillus requires a trace of hzmoglobin for its growth, an orgaiiism, in order to be pathogenic, may require a special substance which may be present only in a certain species, or only in certain tissues of a given species. In this way Ehrlich explained the special predilection of organisms for certain tissues ; for example, that of the smallpox virus for epithelium, or of the virus of hydrophobia for the nervous system. An athreptic condition, consisting in diminished avidity of the receptors, may also be developed in various ways ; for instance, the diminished virulence of an organisni for one species brought about by its growing in the tissue of an animal of a different species, the immunity of a parasite to a drug, or drug-fastness (vide injTa). It is thus seen that Ehrlich’s views with regard to cancer are also dominated by the aide-chain theory. The researches on this subject, which were published from his Insti- tute, were both numerous and important, and, while he had able co-workers, his directing influence is always manifest.

The last years of Ehrlich’s life, from 1903 onwards, were occupied chiefly with researches on the parasiticidal action of various synthetic products, and his side-chain theory was extended to explain the phenomena observed, these observations and speculations culminating in the discovery of salvarsan in 1909. His first experiments were with trypanosomes, and he found that various compounds had a para- siticidal effect in the living body, one of the most striking being that of trypan-red, a single dose of which cured a mouse “ fatally ” infected with the parasite of mal de cameras. I n the course of further investigations, he found that when a relapse occurred after continued treatment, the sterilising effect having been incomplete, the infecting organism had acquired a resistance against t be particular therapeutic agent originally used. Extending his observations to a great many diflerent compounds, he established the important fact that the resist- ance or “ fastness ” t o a particular cornpound applied to other para- siticidal compounds of the same chemical group, but not to those

OBITUARK 357

belonging to other groups. There could Le developed in this way different strains of trypanosomes, drug-fast to different chemicdal groups : for example, (1) the arsenic compounds ; (2) nzo dyes of the benzidiii group, including trypan-red and trypan-blue ; (3) certain basic dyes, in- cluding para-fuchsin, etc. In treating an infection, it was thus possible to get an increased therapeutic effect by using together nienibers from the different groups, polypharmacy in this case being justified. He further shoyed that any particular compound entered into eombina- tion with the parasite-corpora non agunt nisi Jxata-and he regarded this as a union between side-chain of the compound and a side-chain or receptor-chemo-receptor-of the parasite. I n this way the chemical substance was parasitotropic. After the drug was fixed to the receptor, the parasite was brought under the action of the poison or toxophore group. Ehrlich believed also that, in the case of these complicated drugs, the binding group was not connected directly with the toxophore group, but that the two were linked together as side- chains to a central molecule. Thus in salvarsan the amido and the phenol groups bring about the maximal affinity for the parasite, while tlie toxophore group is the arsenic group, these being united by the benzoI group as side-chains of the same. The results mentioned then with regard to drug-fastness indicate that any given parasite has various binding groups or chemo-receptors, and Ehrlich found that drug-fastness occurs when there is a diminished affinity of the receptors for the particular substance : the condition is an example of athrepsy, not of active immunity. In this way Ehrlich extended to synthetic products his views on the constitution of bacterial toxins and their mode of action. There is, however, one important difference, namely, that anti-substances cannot be developed to the former. This is a fundamental difference, and Ehrlich offered in explanation the view, that the cell-receptors by which the synthetic substances are bound have " less independence " than those which bind toxins ; they are of the sessile order and are not thrown off into the circulation.

But the substances in question also combine with the tissues-with their clierno-receptors-and act as cell-poisons, that is, they are organo- tropic as well as parasitotropic. By his early work Ehrlich had found that various dye-stuffs had a definite distribution when intro- duced into the body, and his subsequent investigations showed that localised lesions might be produced by such substances. One of the most striking examples is the production of a lesion in the vestibular nerve of the mouse, resulting in turning movements like those of the Japanese dancing mouse. The tendency for atoxyl and allied arsenic compounds to affect the optic nerve is another example of the same kind. He further showed how the toxic effect of a compound, e.g., phenyl-arsenic acid, might be altered more than a hundredfold by varying the group by which i t is fixed to the tissues-by introducing a

24-!L. OF PATB.-ToL. \\.

358 FA UL EHRLICH.

chlorine group, a hydroxyl group or a cyanogen group, as the case might be. With these facts as a basis the therapeutic problem came to be, how to vary the fixing groups so as to obtain a maximum effect on the parasite and a minimum effect on the tissues.

Amongst the chemotherapeutic agents studied, the arsenic com- pounds occupied the most important place. Atoxyl had been intro- duced as a trypanocidal agent by Breinl and Thomas of the Liverpool School, and a further study of its nature and mode of action was carried out in the Frankfnrt Institute. Ehrlich, along with Berthein, showed that this substance was not an anilide as was supposed, but amido-phenyl-arsenic acid, .a body which is capable of giving rise to a great number of new compounds. I n this substance arsenic is present in the pentavalent form, and it was found that its parasiticidal power was much increased when the arsenic was reduced to the trivalent form, and that the toxic action on the tissues, which the substance still possessed, was greatly diminished when two molecules were combined through the arsenic group. A great many modifications were manu- factured and tested, and a t last salvarsan (dioxydiamido-arsenobenzol) was reached, as the substance which satisfied best the requirements, namely, great parasiticidal effect with the minimum of toxic action on the tissues. The experimental investigation of the properties of salvarsan showed that it had extraordinary spirillicidal properties ; for example, in spirillosis of fowls a complete cure was effected with from the fiftieth to the hundredth part of the dosis tolerata. Having satisfied himself also of its relatively non-toxic action on the tissues, Ehrlich extended its application to syphilis. I n carrying out this long series of researches, he had not only trained pathologists and chemists as his collaborators, but also had a t his disposal the best resources of the synthetic chemical industry of Germany. Was any modification in the substance desired, the new conipound was quickly supplied. The magnitude of the operations involved in the investigations was unique, and an indication is given by the fact that the evolution of salvarsan from atoxyl occupied a period of about four years, and that during this time upwards of two hundred closely allied substances were fully tested.

No one appreciated more fully than Ehrlich the difference between cure of infections experimentally produced and the cure of a long- standing disease with various lesions, such as is syphilis in the human subject. Although he took comparatively little interest in clinical medicine, he had a wonderful grasp of the problems to be faced-the possibility of further damage when certain lesions were present, as well as the possibility of incomplete sterilisation of the tissues, and the development of a resistant strain of the parasite-and he has given in a masterly way a discussion of the whole question from the practical point of view. The methods of administration had to be arranged, the doses fixed, and the various contra-indications defined. With what

OBITUARY: 359

success these ends have been obtained is now known to everybody. The discovery, we may rather say the invention, of salvarsan, and the whole series of researches which led up to it, together constitute a work which in some respects stands unequalled in the history of medical research.

Although, as we have seen, the subjects of Ehrlich’s investigations have been very varied, a unifying principle can readily be traced throughout his work. Running through it from beginning to end like a thread, as some one has said, is the question of the relation of chemical substances, natural or synthetised, to animal cells. This is seen in the domains of haematology, bacteriology, and serology, cancer research, and specific chemo-therapy. Originality marks his start in research, as it does all his subsequent progress-no one owed less to those who had gone before. Like Pasteur he could not be claimed by any one science; he found his field of labour for himself, and worked in it consistently and confidently. It is a long way from the staining of leucocytes to the discovery of salvarsan, just as i t is from the structure of crystals to inoculation against hydro- phobia. Yet in both cases step seems to follow step in natural sequence. With originality of conception and boldness of attack, Ehrlich’s work is marked in equal measure by imaginative power. Every phenomenon, every result was visualised, and new possibilities, new lines of investigation, were seen in advance. This faculty of visualising explains his abundant use of similes and metaphors in his writings, his liking for striking and epigriimmatic phrases. To those conversant with his works, the numerous wvrds which he coined seemed the shortest and most convenient way of indicating the sub- stances or their properties he was dealing with, but to others, equally in- telligent, they rather provecl an obstacle to the ready comprehension of his views. The activity of his imagination led him soinetimes to formulate a theory too rapidly. For example, his view as to the “ amboceptor ” constitution of immune-body is expressed in his first communication on hmnolysins, and, whether it be right or wrong, it cannot be regarded as justified by the facts at his disposal. Yet, once adopted, i t had to be strenuously defended. Ehrlich could hardly be considered ideally tolerant of criticism, though this was largely due to the unintelligent and personal attacks levelled against him. Nevertheless, it is a matter of regret that he put so much value on the recognition of some of his views. After all, truth needs little defence, and nothing can affect the final issue.

Ehrlich was a man of great personal attraction, essentially kindly and human, and keenly appreciative of the work of others. His earlier work was performed practically single-handed, but each successive step brought him more and more co-workers, until a t last he was surrounded by a band of investigators such as has hardly been equalled. He was an indefatigable worker, and in late years his

intellect, so far from showing any signs of impairment, seemed rather to gain in activity and power of concentration. His work received early recognition in this couIitry, a matter of no small satisfaction to him. He gave the Croonian Lecture in 1900, the Harben Lectures in 190’7, and that most remarkable address on Chemo-Therapy a t the International Medical Congress in London in 19 13. It is proverbi- ally difficult for a man’s contemporaries to determine his scientific status. But we believe that Ehrlich must be with the greatest, how- ever small that company may be.

ROBERT MUIR.