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tainly broad enough, and gives any school the right to importany piece of apparatus, no matter how simple or how complex,cheap or expensive, provided it is to be used in making scientificobservations or exhibiting the action of natural forces. It wouldseem that the Treasury Department has clearly no right to inter-pret the law as indicated by the circular in question and by theiractions as well. The science teachers of this country should vig-orously protest against such interpretation and bring all possiblepressure to bear through the press and Congress to the end thatthe law may be rationally administered and that the advancementof scientific instruction may not be handicapped by the Chinesewall of exclusion recently erected at the Custom HOUSQ.

WHAT IS AN INFECTIOUS DISEASE?

BY W. :EL MANWARING.,Johns Hopkins Medical School.

Fornerly Professor of Physiology and Hygiene, State Norma School, Winona, Minn.

For several years I have been trying to find a simple methodof demonstrating the nature of infection to secondary and ’gram-mar-school pupils. It is desirable that there be a widespread un-

derstanding of the nature of contagious diseases, in order thatsanitary and hygienic actions of medical boards and boards ofhealth may have a meaning in the mind of the public at large.I take it that the creating of this understanding is one of themost important duties of the public schools.

At first, I tried various devices, all borrowed more or lessdirectly from the bacteriological or pathological laboratories, butwith unsatisfactory results. The inoculation of a mouse with’bacillus anthracis and the demonstration, after death, ;of theorganism in blood of the animal by cover-slip and staining methods,did not convey to the minds of the pupils the vivid conceptions Iwished. The red-and-blue pictures seen under the ’compoundmicroscope had little meaning to most of them. The examinationof diphtheritic membrane and of consumptive sputum were open

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to the same objections; special staining methods had to be, used, andthat and the compound microscope forced the thing off into aland of mystery and imagination.

What I wanted was a device to bring the facts before themin a vivid and picturesque manner, without staining or culturemethods or any of those processes that to the scientist are sosimple, but which are so enigmatic to the untrained pupil.

One year, I tried introducing cyclops into a jar swarmingwith vorticellae. Before many days, some of the cyclops were cov-ered with a squirming, jerking mass of vorticellae, easily seen bya simple lens. By a .stretch of the imagination, the mass mightbe likened to an infection. But the device was unsatisfactory;there was not elasticity enough in it; it did not readily lend itselfto the development of the subject.

I have, however, found a device that fulfills, to a quite satis-factory degree, most of the requirements. The material is abun-dant, every boy and girl can make his observations for himself, itlends itself readily to questions as to methods of prevention, isola-tion, sterilization and the like, and requires nothing in the line ofmedia, stains or compound microscopes.

In the fall of the year, every boy and girl has seen, lyingabout or hanging to the ceiling or window pane, the swollenbodies of flies, dead from the fly fungus. The white dust-likespores, the bloated body, the alternate white and black bands of theabdomen, have been noticed by most of them. Then is the -timeI give my lesson on ^The Dead Fly.^ A simple magnifying glassshows the fungus that killed the insect and the spores about it,and questions like: ^How might the fungus have gotten on thefly in the first place ?^, "If. you wanted to kill off all the flies in theroom with the fungus, how would you go to work to do it?5’, ^Ifyou found a dead fly and wished to prevent the other flies fromgetting the disease, what would you do?^ and the like, bring outall the essential facts of contagion and disinfection. When this is

done, the step to the conception of bacteria, infection and prophy-lactic measures is simple and is taken by the pupils almost in-stinctively and with no forcing on my part.

I commend this device to all live teachers of elementary

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physiology and hygiene, as I believe it to be the best one for thepurpose now before the teaching profession.*

INTRODUCTORY METEOROLOGICAL EXPERIMENTS.

WM. H. SNYDEK.

There are few schools at the present day which do not at somepoint in their course consider the elementary principles of meterol-ogy. Very often this work is undertaken without any previousknowledge of physics or with an indistinct remembrance of .someexperiments and discussions which took place in the dim past. Itis therefore almost always necessary to consider the subject denovo and develop all the necessary conceptions. If meteorology isever to be understood, there are a few fundamental principleswhich must be firmly grasped and upon which as a basis the rest.of the subject must be built. I have endeavored to lay this founda-tion by means of the following simple experiments. These experi-ments cover about all the considerations necessary for elementarywork and can be understood by pupils without previous scientific-training.

I. Air Has Weight.�Take a large bottle and weigh it full of air:md then weigh again with as much of the air exhausted as possible.The difference of the two weights, which will be appreciable on a

pair of ordinary laboratory scales, will be the weight of the air removed.The volume of this removed air can be tound by opening the mouth of-the exhausted bottle under water and sinking the bottle as the waterruns in, thus keeping the level of the water outside and inside the bottlethe same. The weight of the water in grams which flows in is approxi-mately the volume of the air removed in cubic centimeters.

II. Air Eixerts Pressure.�Take a tube about eighty centimeterslong, open at both ends, and over one end slip a short piece of tightly-fitting rubber tubing which can be completely closed by a pinch-cock.Having closed the rubber tube, as nearly as possible at the end of theglass tube, fill the long tube with mercury and invert in a cup of-mercury. If the connections are tight an ordinary mercurial barometercolumn will be formed, showing that some force must hold the mercuryup. To the average boy or girl, however, pressure nreans an active

*Those interested in the fly fungus will find a short description of it in the POPULARSCIENCE NEWS for December, 1901, and in the Literary DIGEST for Dec. 28, 1901.