METHODS OF STUDYING BACTERIA 43 



Other proteins, like beef-serum, egg-albumin, red blood- 

 corpuscles, have produced similar results, varying doses and 

 periods of incubation. Human beings may be sensitized by 

 single injections of horse-serum. 



Hay-fever, asthma, puerperal convulsions, and sympathetic 

 ophthalmia partake of the nature of anaphylactic reactions, 

 and the peculiar intolerances to certain articles of food may 

 be better explained by the same theory. 



The sudden attacks of collapse and death which have 

 followed the injection of even small doses of antitoxins made 

 from horse-serum are believed to come from this condition 

 of hypersensitiveness. 



The use of globulins instead of the entire serum has lessened 

 the danger from anaphylaxis. 



CHAPTER V 

 METHODS OF STUDYING BACTERIA. MICROSCOPE 



Microscope. Most clinical instruments now on the mar- 

 ket have all the necessary appliances for bacterial examina- 

 tion. Three objectives are advisable 16 mm. (^ inch); 

 4 mm. (>6 inch); 2 mm. ( T V inch). It is not so much 

 required to have a picture very large, as to have it sharp and 

 clear. 



Oil-immersion Lens. The penetration and clearness of 

 a lens are very much influenced by the absorption of the rays 

 of light emerging from the picture. In the ordinary dry 

 system many of the light rays, being bent outward by the air 

 which is between the object and the lens, do not enter the lens, 

 and are lost. By interposing an agent which has the same 

 refractive index as glass, cedar-oil or clove-oil, for example, 

 all the rays of light from the object enter directly into the lens. 



The "homogeneous system," or oil-immersion lens, con- 



