and Laboratory Methods. 1733 



may occur in the nose, but usually appears as abscesses, inflammations and 

 necroses, in the skin and muscles resembling carbuncles closely. When a 

 positive diagnosis cannot be made from a cover-glass preparation, introduce into 

 the peritoneal cavity of a male guinea pig a bit of the suspected tissue. If it is 

 a case of glanders the testicles will begin to swell in thirty hours, the skin will 

 become red and shiny, and pus will form, often breaking through the skin. This 

 result is characteristic and positive of glanders. 

 Harvey Medical College. WiLLiAM H. Knap. 



The Technique of Biological Projection and Anesthesia of 



Animals. 

 II. 



AVAILABLE LIGHTS AND THEIR LIMITATIONS. 



In projection work of all kinds the most important factor is the light and its 

 proper adjustment to the object. A safe rule is that the light should be stronger 

 than is required for the magnification ordinarily used and capable of being 

 developed at the will of the operator up to the maximum intensity needed for 

 more difficult objects. Applying this rule to such sources of light as oil, gas 

 with Welsbach burner, incandescent electric and acetylene, all of which are use- 

 ful in producing certain grades of lantern slide pictures, it is evident that they 

 can be used only with lantern slide projection lenses, and that they will fail to 

 give satisfactory results with projection microscopes. Nevertheless, many instruc- 

 tive and interesting experiments upon small animals, measuring from one-quarter 

 inch to several inches in length, are possible with the better lights of this class. 

 With a one-fourth size projection lens, the magnification on the screen, placed at 

 a distance of thirty feet from the lantern, is from fifty-five to sixty-five diameters. 

 Small fish, especially goldfish, tadpoles, many aquatic larvae, nymphs of dragon- 

 fly, leeches, earthworms, small frogs and tree frogs, crayfish and similar types, may 

 thus be made to exhibit their forms, motions, more or less of their internal organs, 

 e. g., the alimenatary canal, respiratory and circulatory systems, and even the 

 circulation of the blood, if observed from' near the screen. The methods of 

 preparation of live animals, so that they may be used in the lantern in place of 

 lantern slides, will be explained in a later article. The arrangement of light, 

 condensers, projection lenses and screen is the same as for lantern slide work. 

 Anesthesia with chloretone is a valuable addition when the study of the circula- 

 tion of the blood and internal organs is undertaken. 



The lowest power artificial light which is strong enough to use with projec- 

 tion microscopes is oxyhydrogen. This gives far better results than the lights 

 referred to above with all forms of work mentioned in the preceding paragraph, 

 and is also suitable for microscopical projection of reasonably transparent objects 

 up to a power of about one-thousand diameters. To reach this limit, however, 

 careful attention must be paid to the adjustment of the jet and lime cylinder and 

 their distance from the pair of condensers used for lantern slide work, also to a 



