PRODUCTS OF THE GROWTH OF BACTERIA. 129 



Bacteria which are able to decompose cellulose are found 

 in the stomachs of ruminant animals. Although it is doubt- 

 ful whether the products of cellulose decomposition have 

 any nutritive value, the process is useful in effecting a sub- 

 division of the coarse food, consisting of grass, hay, and 

 the like. 



Some bacteria have the power of decomposing neutral 

 fats into fatty acids and glycerin, after the manner of the 

 fat-splitting ferment of the pancreatic juice. 



The end-products which result from the growth of bac- 

 teria upon albuminous nutrient media are very numerous. 

 They are complicated and not well understood. Among 

 these end-products may be mentioned peptone, indol, skatol, 

 phenol, leucin and tyrosin. Nearly related are the toxins, 

 which play an important part in the production of disease 

 by pathogenic bacteria. In the decomposition of urine by 

 bacteria the urea is converted into ammonium carbonate. 



The formation of indol in cultures is an important pecu- 

 liarity of certain bacteria, which may be tested as follows : 

 The bacteria are cultivated in Dunham's peptone solution or 

 in dextrose-free bouillon; after twenty-four to forty-eight 

 hours the test may be made. Add ten drops of concentrated 

 sulphuric acid; the development of a rose-color indicates 

 the presence of both indol and nitrites. If no rose-color 

 forms, to another tube add, first i c.c. of a o.oi per cent, 

 solution of sodium nitrite, and then the sulphuric acid. The 

 development of a rose-color indicates the formation of indol 

 but not of nitrites. If there is no rose-color, no indol has 

 been formed. The color appears usually in a few minutes, 

 but it may only develop after a somewhat longer time. Con- 

 trol tests must be made upon tubes of the same peptone 

 solution but which have not been inoculated. The reaction 

 may be hastened by warming slightly. The value of this 

 reaction will be understood when, to give one illustration. 



