572 J. E. RUSH AND G. A. PALMER 



it was desired to examine several organisms isolated from a 

 water supply and upon which confirmatory work for Bad. coli 

 was necessary. 



Inoculations of the same batch of gelatin were made in dupli- 

 cate and controls from the same batch of media were used. In the 

 making of the media the standard procedure^ was used, i.e., 

 10 per cent gelatin was made and the final reaction was adjusted 

 to + 1 on the phenolphthalein scale. As above stated inocula- 

 tions were made in duplicate of the cultures to be examined — 

 one set was placed in the 20°C. incubator, following the generally 

 accepted method of procedure and observations were made 

 after ten and fourteen days (as recorded below). The other 

 set was placed at 37°C. for four days and then transferred to 

 the 20 °C. incubator for twenty-four hours after which the re- 

 sults were recorded. 



It is a well recognized fact, that in a number of gelatin stabs 

 exposed to 20°C. the longer the time of exposure, the greater 

 will be the percentage showing liquefaction. This has been 

 definitely shown by Gage and Phelps- but so far as we are aware 

 the relation between a certain time (ten to fourteen days) at 

 20°C. and the combination incubation, first at 37°C. and later at 

 20°C. has not been determined. Prolonged high temperature 

 will keep gelatin from sohdifying again but this did not obtain 

 here with exposure of the gelatin to 37°C. for four days, as e\'i- 

 denced by the fact that the controls on the media, while hquid 

 after removal from the 37°C. incubator were again solid when 

 removed from the 20°C. incubator after a further exposure of 

 twenty-four hours. 



This gelatin inoculation is made, as is well recognized, for the 

 simple purpose of determining the presence or absence of cer- 

 tain proteolytic enzjanes, namely, gelatinases. As in other 

 biochemical reactions, the rate of reaction is influenced by 

 certain factors in the environment and one of the most import- 

 ant factors is that of temperature. The cultures experimented 



1 Standard Methods for Examination of Water and Sewage, 1920. 



2 Gage and Phelps. Quoted by Prescott and Winslow. Elements of Water 

 Bacteriology. John Wiley and Sons. 1915. 



