22 SELMAN A. WAKSMAN 



here the toxic effect of the nitrite may become apparent, par- 

 ticularly with some sources of carbon, so that in the presence 

 of 0.05 per cent of NaN0 2 , most of the species tested made a 

 very good to excellent growth with glycerol as a source of car- 

 bon, while the same species produced only a scant growth in the 

 presence of glucose. When the nitrite content of the medium is 

 still further increased, the growth ceases entirely or is only very 

 limited. 



In the previous experiments on the action of the actino- 

 mycetes upon different proteins, only purified native substances 

 were used. To study further the action of these organisms upon 

 protein-rich substances, they were grown on gelatin (15 per cent 

 in distilled water), with and without one per cent of starch, on 

 milk and on glucose broth (1 per cent peptone, 0.5 per cent 

 meat extract and 1 per cent glucose). The results are reported 

 in table 6. 



Here again no greater importance should be attached to the 

 data presented in table 6 than to any other set of biochemical 

 data with a group of microorganisms, where only one or two 

 tubes for each organism are studied. But, although the results 

 are not absolute, a comparative study of the data will be of 

 interest. These experiments were repeated several times at 

 different temperatures and, although a great deal of variation 

 was obtained, the comparative results hold true as a whole; 

 and it really makes very little difference, when such a variable 

 group of organisms is studied, whether one species accumulates 

 25 or 35 mgm. of NH 2 -N in 10 cc. when grown on a 15 per cent 

 gelatin solution. All the species studied cause a splitting of 

 gelatin, peptone and milk proteins to a greater or less extent, 

 but the organism that produces a maximum splitting of the 

 gelatin does not necessarily split the maximum of peptone, 

 casein and other proteins. As we might expect, however, many 

 species that split one protein actively, also split the others 

 actively. The amount of ammonia accumulated in milk is 

 relatively large, particularly for the organisms which are active 

 proteolytically; this is due to the long incubation period at a 

 rather high temperature; in a shorter period of incubation the 



