THE CHEMISTRY OF BACTERIA, 91 



mentioned among the acid products. Amido-acids, sucli 

 as leucin, tyrosin, etc., may be formed in protein decom- 

 position. 



The fact that some bacteria readily give rise to acids, 

 whereas others do not, can be made use of for the purpose 

 of recognition. The reaction can best be observed by 

 coloring the medium with some litmus solution. When 

 acids are produced the litmus colored medium will assume 

 a red color, otherwise it remains blue. The bacillus of 

 tetanus, for example, does not redden glucose gelatin, 

 whereas that of malignant edema does. Again, the 

 typhoid bacillus does not produce an acid when grown on 

 media which certain milk-sugar, whereas the colon bacillus 

 does. 



Alcohols. — In the decomposition of carbohydrates by 

 bacteria several alcohols may form, but the amount is 

 usually very small. Ethyl and butyl alcohols have been 

 frequently met with. Glycerin is produced in small quan- 

 tity by the yeast-plant. Phenol or carbolic acid, which is 

 liberated in the putrefaction of proteins, belongs under 

 this head. 



Gases. — The gaseous products of bacterial growth are 

 of considerable interest. It has already been indicated that 

 the different bacteria give off, or exhale, variable amounts 

 of carbonic acid. It may happen in such cases that no 

 visible evolution of gas occurs. Usually, however, the 

 presence of bubbles in the liquid or solid media indicates 

 the active generation of gaseous products. An increased 

 formation of gas is observed when glucose is added to the 

 culture medium. 



The carbohydrates, in general, are very prone to give 

 rise to gaseous products when acted upon by micro-organ- 

 isms. Carbonic acid represents the final form to which all 

 organic substances are eventually changed. It is, conse- 



