BIOLOGIC CHARACTERS. 197 



all the changes that occur in the growth on successive 

 days. 



Growth in Bouillon. Observe the nature of the 

 growth in bouillon. Note whether the fluid shows tur- 

 bidity or not, as well as the extent and distribution of 

 this alteration. Note whether any sediment is being 

 formed, as well as the nature and amount of such sedi- 

 ment. Does the organism form a definite growth (pel- 

 licle or scum) on the surface of the bouillon ? What is 

 the character of the pellicle ? Is is readily dislodged, 

 and, when dislodged, is it replaced by a new pellicle ? 

 Note whether the color of the medium has become 

 altered. Note the manner in which the appearance of 

 the culture changes on several successive days. 



Growth in Litmus-milk. Observe the nature of the 

 growth in litmus-milk. Has the reaction of the medium 

 become altered? To what is such alteration attribu- 

 table? Note whether there is precipitation of casein. 

 Record the extent and rapidity with which this altera- 

 tion takes place, as well as the reaction of the fluid 

 while the change is being produced. Is there any evi- 

 dence of the subsequent liquefaction of the precipitated 

 casein ? Has the litmus been altered in any manner 

 except as shown by altered reaction of the medium? 

 In what part of the tube has such alteration of the 

 litmus commenced? If the litmus has been decolorized, 

 is it possible to restore its color by the admixture of air 

 with the fluid? Note the manner in which the appear- 

 ance of the medium changes on successive days. 



Growth in Special Media. The special culture-media 

 may be employed to ascertain additional biologic char- 

 acters of an organism, such as the production of indol, 

 reduction of nitrates to nitrites, the formation of ammo- 



