ON DECREASING THE EXPOSURE NECESSARY FOR 

 THE GELATIN DETERMINATION 



J. E. RUSH AND G. A. PALMER 



Sanitary Engineering Department, Carnegie Institute of Technology, Pittsburgh, 



Pennsylvania 



Received for publication March 8, 1921 



Some time ago, one' of us (J. E. R.) was advised of the fact 

 that there was a more rapid method for determining the ability 

 of organisms to Hquefy gelatin than the routine one, in use in 

 most laboratories, namely, subjecting the gelatin stab to a tem- 

 perature of 20°C. for ten or fourteen days after inoculation and 

 then noting the results. Search of the literature failed to reveal 

 any description of the more rapid method which was described 

 as incubation at 37°C. for four days followed by twenty-four 

 hours incubation at 20°C. after which the results were recorded. 



Many reasons recommend the latter procedure providing the 

 results obtained are identical with those recorded by the 

 present recognized procedure. Among such reasons we might 

 enumerate : 



1. The saving of time (five days requirement as contrasted 

 with fourteen days). 



2. Earlier liberation of test tubes from the incubator (which 

 in a busy laboratory is an important factor) . 



3. Necessity of less incubator space to meet the requirements 

 of any laboratory (in some cases dispensing altogether with the 

 use of a 20°C. incubator). 



As search of the literature failed to reveal any information 

 on this point it was determined to test out the two methods 

 simultaneously on the next set of cultures which came into the 

 laboratory and upon which confirmatory work (including the 

 gelatin reaction) was to be done. This opportunity came when 



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JOURNAL OP BACTERIOLOGT, VOL. VI, NO. 6 



