26 SELMAN A. WAKSMAN 



cussed in detail elsewhere (Waksman, 1919). To get an insight 

 into the rapidity of the proteolytic action of some species on the 

 milk proteins, as affected by temperature of incubation and 

 mode of action of the different species, the following experiment 

 was conducted: 



A series of tubes, each containing exactly 10 cc. of sterile 

 milk, were inoculated with A. griseus and A. exfoliatus, inoculat- 

 ing all tubes as nearly alike as possible. Ten tubes for each 

 species were inoculated at 25° and 10 at 37°. Observations were 

 made daily as to the clotting and peptonization. The amino 

 and ammonia nitrogen of the milk were determined at the end 

 of definite intervals and results calculated back to the total 

 amount. This experiment was repeated. The results are given 

 in table 8. 



The results reported in the table are not sufficient for plot- 

 ting an exact curve, because the average error between the 

 duplicates is greater than should be allowed for accurate work. 

 The importance of using a definite period of incubation for all 

 the groups is brought out clearly: while the strongly proteolytic 

 species produce a continuous splitting of the proteins, the weaker 

 forms may, at an early period, allow a splitting, which will not 

 advance much further. It is also interesting to note that when 

 the period of incubation is long enough the difference in the 

 quantities of amino nitrogen content of the milk and ammonia 

 accumulated approaches to zero. 



The ammonia accumulation by actinomycetes is slow, but 

 increases steadily. When these organisms are compared with 

 molds and bacteria in their power of producing ammonia, an 

 interesting difference is observed. The rapidly growing bac- 

 teria and molds allow a rapid accumulation of ammonia, which 

 soon reaches its maximum as a result of the metabolism of these 

 organisms; the slow growing actinomycetes allow only a slow 

 accumulation of ammonia; if a long enough period of incubation 

 is allowed, the amount of ammonia may even become as large 

 as that produced by the active proteolytic bacteria and molds. 



