1202

factor is introduced at the end of -the calculation. In the

case of cattle observations were recorded by the fifth EarlSpencer, which show a range of time extending from theH20th to the 313th day after insemination, but as, accordingto Dr. Hart, calves are to be regarded as premature beforethe 260bh day, the period of variation is rather less than this.If these figures are also reduced to a curve, again a

fairly symmetrical figure is produced, the maximum

number of births lying between the 284th and 285th

days. It seems legitimate to conclude that, as mightbe predicted in a vital process, the duration of gesta-tion is not a rigidly fixed period, while the greaterrange of variation in cattle as compared with sheepmay be explained by assuming that in -the former two ovamay be shed at intervals of three weeks, and that either oneor other may be fertilised at any particular act of coitus.Figures as to the duration of human pregnancy have beencollected by several observers, notably by von Winckel andby Reid, who calculated respectively from the first and lastdays of the preceding menstrual period. Curves preparedfrom their data again show fair symmetry, the range foundby von Winckel being from the 258th to the 313th day, andbv Reid from the 252nd to the 316th. The maximum number

fell in the former author’s experience between the 282nd and289th days after the first day of the last menstruation ; inthat of the latter between the 276th and 279th day after thecessation of the period. It is clear that we are not in a

position at present to predict with any accuracy the probableduration of an individual pregnancy, and that further

observations are desirable. Dr. Hart suggests that moreexact results might be obtained officially under the InsuranceAct " if the dates of beginning and end of the last period ofmenstruation and the date of labour were recorded on the

official cards which have to be prepared in order to establisha claim to maternity benefit.

ALTITUDE AND BLOOD VOLUME.

THE increase in the number of red blood corpuscles inanimals and man living at high altitudes is a well-establishedfact. Animals living in Mexico at 3700 metres have doublethe normal number of red corpuscles, and Viault found6 to 9 millions per cubic millimetre in Peruvians dwellingat over 4000 metres. Miintz kept rabbits in the summit

of the Pic du Midi for seven years, and found that i

the iron percentage of the blood increased from 40’3on the plain to 70’2 milligrammes at the summit.There is also an increase in the haemoglobin percentagein the blood. These results have been ascribed to variouscauses. This week we print a communication on theEffect of Altitude on Blood Volume by Professor G. Dreyerand Dr. E. W. Ainley Walker. From this it appears thatthere are also definite changes in the blood volume, whichfollow definite laws. Bohr observed that diving birds whichremain several minutes under water have double as muchblood as ordinary birds. The authors have analysed the"almost inexhaustible wealth" of the information recorded

by Abderhalden from observations on rabbits kept at

St. Moritz from four and a half to eight weeks, 1856metres above sea level, in 1902, and they are led to

the conclusion that the change of volume which occurswith a particular change of barometric pressure is pro-

portional to the area of the body surface in differentindividuals of a given species. The blood volume is

diminished by an amount exactly proportional to their bodysurface. In the St. Moritz rabbits the diminution of blood-

volume was nearly 11 per cent. ; the haemoglobin shows anincrease and the number of red cells a parallel increase. The

increase of the haemoglobin reaches 11’ 7 per cent. of the totalhsemoglobin. This shows that there is an active new formation

of blood during a temporary residence of some weeks at highaltitudes. The increased oxygen capacity is as regards onehalf due to concentration of the blood and as to the otherhalf to new formation of haemoglobin and red cells. In the

early days of the sojourn the whole change is due to diminu-tion of the blood volume. The authors are not in agree-ment with some of the conclusions of Douglas, Haldane,Henderson, and Schneider from their observations made onPike’s Peak (3386 metres). When the St. Moritz rabbits

were brought back to Basel the blood volume reached theBasel normal in four days, and after the third day andonwards the daily fall in oxygen capacity ran parallelto the fall in percentage haemoglobin. A formula is

given for the calculation of the volume of blood in

mammals, and the authors find the same formula applicableto certain birds which they name. This relation between

blood volume and surface area of the body of mammals andbirds is related to the fact that they are homoiothermalanimals or animals of constant temperature. In poikilo-thermal animals, such as a frog and lizard, the blood volumeis neither proportional to the body surface nor to the bodyweight. The blood volume increases as the animal growsheavier, while in warm-blooded animals there is a steadydiminution. Professor Dreyer and Dr. Ainley Walker alsofind that the ratio of the weight of the heart muscle-indifferent species-to the total oxygen capacity is approximatelyconstant from species to species in a number of instances.One of the other interesting results is the comparison of thehare and wild rabbit to show the importance of life andmuscular activity as a factor in determining the amount andthe distribution of the haemoglobin in the body. Animalswith a high haemal haemoglobin have usually dark-colouredmuscles and a high hmmoglobin percentage in their skeletalmuscles ; those with a lower haemal haemoglobin percentagehave pale muscles. The hare as compared with the wildrabbit has remarkable speed, greater endurance, higherhaemoglobin percentage, darker muscles, a heavier heart, anda larger aorta. The hare has more than double the amount

of blood, 30 per cent. more haemal haemoglobin, and aboutthree times as much heart muscle as a wild rabbit. These

and other facts recorded in this communication offer fruitful

suggestions for more extended investigation into the im-

portant question of blood volume.

AN INSTRUCTIVE MISTAKE.

ONE of the valuable features of the B1’itish Journal of’2crgeri is a series of cases published anonymously under theheading of instructive Mistakes." In the following casea distended saccule of the bladder was mistaken for a caecal

volvulus. A man, aged 79 years, in fair general health, whohad not suffered from any urinary symptoms, was seizedwith abdominal pains and urgent vomiting, which was

copious and projectile. The pains were paroxysmal andreferred to the lower abdomen, especially to the right iliacfossa, where a firm elastic swelling could be seen and felt.During the pains it hardened palpably. It was only rela-tively dull on percussion, and there was no obvious hypo-gastric fulness. The bowels had acted regularly, and afterenemata fasces and flatus ceased to be expelled. Purgativescould not be retained on the stomach and therefore failedto act. The prostate was much enlarged, but there was nosystitis. As urine was passed occasionally and instrumentalud did not appear to be required no catheter was passed. Therewas no general abdominal distension or tenderness. Volvulus)f the csecal region was diagnosed and laparotomy was per- ,

formed, when the swelling was found to be a large distendediaccule of a deformed bladder. The whole length of thentestines was examined methodically without finding any)bstruction. An elbowed catheter was passed and the