l8o GENERAL BIOLOGY OF MICRO-ORGANISMS 



Physiological Tests. — Specific tests for a simple physiological 

 character require less skill and care in their observation, and are 

 widely ijsed. Cultivation in a fermentation tube of sugar broth 

 as a test of ability to form gas from the sugar, titration of sugar- 

 broth cultures to ascertain the abiUty to produce acid from various 

 sugars, chenjical test for the presen'ce of indol and of ammonia in a 

 culture in peptone solution, observation of the ability to hemolyze 

 or discolor blood mixed with the medium, and the ability to fer- 

 ment glycerin, these are some of the valuable simpler tests. 

 Cultivation in niilk is a somewhat more complex test, as a variety 

 of fermentable substances is offered the microbe, increasing the 

 diflSculties of interpretation but also increasing the variety of phe- 

 nomena which may occur. 



A convenient outline to use in making morphological and 

 physiological observations upon bacteria and in recording the re- 

 sults, has been prepared by a committee of the Society of American 

 Bacteriologists. Many features of this will be found of assistance 

 in the study of new or unknown bacteria, especially saprophytic 

 forins. A copy of the revised descriptive chart is inserted along 

 with a copy of the earlier chart of 1907. 



