202 BIOLOGY AND TECHNIQUE 



Proteolytic 6 enzymes may also be determined by growing the 

 bacteria upon fluid media containing albumin solutions, blood serum, 

 or milk serum, then precipitating the proteins by the addition of 

 ammonium sulphate (about 30 grams to 20 c.c. of the culture fluid) 

 and warming between 50 to 60 C. for thirty minutes. The pre- 

 cipitate is then filtered off, the filtrate made strongly alkalm with 

 NaOH, and a few drops of copper sulphate solution added. A violet 

 color indicates the presence of pepton proving proteolysis of the 

 original albumin. 



DIASTATIC ENZYMES. The presence of diastatic ferments may be 

 determined by mixing broth cultures of the bacteria with thin starch 

 paste. It is necessary that both the cultures and the starch paste 

 be absolutely free from sugar. After remaining in the incubator for 

 five or six hours, the fluid is filtered and the filtrate tested by methods 

 used for determining the presence of sugars. 



INVERTING FERMENTS. Inverting ferments are determined by a 

 procedure similar to the above in principle. Dilute solutions of cane 

 sugar are mixed with old cultures or culture filtrates of the respec- 

 tive bacteria and the mixture allowed to stand. It is then filtered, 

 and the filtrate tested for glucose, preferably by Fehling's solution. 



ANIMAL EXPERIMENTATION 



In the study of pathogenic microorganisms, animal experimenta- 

 tion is essential in many instances. The virulence of any given 

 organism for a definite animal species and the nature of the lesions 

 produced are characteristics often of great value in differentiation. 

 Isolation, moreover, of many bacteria is greatly facilitated by the 

 inoculation of susceptible animals and recovery of the pathogenic 

 organism from the heart's blood or from the lesions produced in 

 various organs. That investigations into the phenomena of im- 

 munity would be absolutely impossible without the use of animal 

 inoculation is, of course, self-evident, for by this method only can 

 the action of bacteria in relation to living tissues, cells, and body- 

 fluids be observed. 



The animals most commonly employed for such observations are 

 guinea-pigs, white mice, white rats, and rabbits. The method of 

 inoculation may be either subcutaneous, intrapleural, intraperitoneal, 



*Hanlcin and WesfbrooTc, Ann. Past., vi., 1892. 



