EXPOSURE FOR GELATIN DETERMINATION 



573 



with, probably represent an average population of those organ- 

 isms found in water supplies and giving a positive presumptive 

 test for Bad. coli, because they are from many sources and 

 sampled under a variety of conditions. 



It should be further recalled that the optimum temperature 

 of these organisms, undoubtedly varied considerably and that 

 they probably exhibited varying degrees of adaptation. In 

 addition, it may well be assumed that the difference between 

 exposure at 37°C. and 20°C. even for a short time would be 

 sufficient to stimulate a gelatinase production in certain forms 

 while inhibiting it in others. That we are probably not dealing 

 with a single enzyme which has the power of gelatin liquefac- 

 tion, and that our problem is thus complicated is evident from 

 certain work on zymology.^ 



The general results of our tests are shown in the table below: 



"Slight" signifies 20 per cent liquefaction or less; "Marked" signifies 25 per 

 cent liquefaction or more. 



CONCLUSIONS 



From the table it will be seen that no very definite statements 

 can be made except that if we desire to get the results (as ordinarily 

 done now) by exposure to 20°C. for ten or fourteen days — these 

 same results cannot be reahzed by exposure to 37°C. for four 

 days and then to 20°C. for one day. 



3 Biochemical Catalysts in Life and Industry. EfTront and Prescott. John 

 Wiley and Sons. 1917. 



