Il8 MANUAL OF BACTERIOLOGY. 



which act like rennet in coagulating milk. Other bacteria 

 are capable of forming sugar from starch. Others have the 

 power of changing cane-sugar into glucose. 



Bacteria which are able to decompose cellulose are found in 

 the stomachs of ruminant animals. Although it is doubtful 

 whether the products of cellulose decomposition have any 

 nutritive value, the process is probably 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 bacteria 

 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 (see Chapter 

 VI.), which play an important part in the production of dis- 

 ease 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 peculiarity 

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

 are cultivated in tubes of dextrose-free bouillon, or in Dunham's 

 peptone solution, preferably the former; after twenty-four to 

 forty-eight hours the test may be made. This consists in the 

 addition of 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. 

 Control tests must be made upon tubes of the same bouillon but 

 which have not been inoculated. The reaction may be hast- 



