186 THE AMERICAN MONTHLY [June 



5. Dip once in two, three, and four, if color is deeper 

 than light pink. 



6. Cover mount with Grabbet's solution two minutes. 



7. Dry and examine as above. 



A one-eight or one-sixth objective, in other words, the 

 enlargement of 400 diameters, with or without eye-piece 

 multiplications, produces a clear field sufficient for diag- 

 nostic purposes. 



Alcohol mixed with fresh sputum in order to pre- 

 serve it, coagulates the albumen which should be softened 

 with a two per cent solution of caustic potash before 

 spreading over a cover-glass. A saturated solution of 

 borax preserves the sputum, liquifies the mucus and does 

 not coagulate the albumen. 



Most cocci take Gram's staining readily. The gono- 

 coccus, however, being an exception, will not take Gram's 

 method, this being one of its main diagnostic features. It 

 takes all the ordinary aniline stains. 



Gram's Solution. — Iodine, 1 part ; Potassi lodidi, 2 

 parts ; Aquas distillat, 100 parts. 



The potash is not indispensable bu't added to facilitate 

 solution. 



2. The color of colonies. — If the individual bacteria 

 in any given species be grown on a suitable soil, such as 

 gelatine, bouillon or potato, there results a mass or col- 

 ony of these minute plants whose size, shape and color 

 afford essential means of. differentiating the organisms, 

 and the bacteriologist uses them for recognizing his min- 

 ute plants just as the chemist uses the behavior of a 

 given substance to identify his still more minute mole- 

 cules. The streptococcus grows into light gray colonies 

 while the staphylococcus produces bright yellow. 



It is only wlien growing in masses that enough color 

 is formed to be visible. Not infrequently are these 

 colored masses so luminous that they can be photo- 

 graphed by their own light when placed in ^ dark room. 



