186 THE AMERICAN MONTHLY [June 



5. Pip once in two, threo, aiul four, it' color is deeper 

 tliati li^lit i)iiik. 



6. Cover mount with Gabbet'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, })roduces a clear field sullicient for diag- 

 nostic purposes. 



Alcohol mixed with fresh sputum in order to })re- 

 serve it, coagulates the albumen which should he 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 excei)tion, 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 ; Aqua' distillat, 100 parts. 



The potash is not indispensable but added to facilitate 

 solution. 



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

 in any giv«m 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, sliape and color 

 allbrd essential means of differentiating the organisms, 

 and the bacteriologist us(>s them for recogui/ing 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 jiroduces bright yellow. 



It is only when 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 theii- owa light when pla(;ed in a dark room. 



