14 SELMAN A. WAKSMAN 



To return back to table 1, we find that when nitrites are pres- 

 ent in the medium as the only source of nitrogen, the amount 

 of growth is less than in the case of nitrates, unless the nitrates 

 are present in very small amounts, otherwise (even in the pres- 

 ence of 0.2 per cent NaN0 2 ), they seem to become toxic, so 

 that the amount of growth is very limited. In the presence of 

 0.2 per cent NaN0 2 , many organisms made a small growth, 

 limited in most cases to a few floccules on the bottom of the tube 

 and only in the case of the organisms that reduce nitrates to 

 nitrites vigorously (A. violaceus-ruber) was the growth more than 

 fair. The question of utilization of nitrites will be discussed 

 later. 



The amides, as stated above, form a very poor source of 

 nitrogen in comparison with the proteins and amino acids. 

 Only a few species made more than a very limited growth, the 

 reaction in the case of urea, either remaining unchanged, becom- 

 ing slightly acid, or, in most cases, turning alkaline; this latter 

 phenomenon is no doubt due to the rapid splitting off of ammonia 

 from urea. In the case of acetamide, the reaction became in 

 nearly all cases more acid, which may be explained by the fact 

 that the NH 2 radical is used up and may be replaced by an OH 

 radical, which may turn the medium more acid. 



The utilization of proteins and amino acids can be followed up 

 in two ways, first by observing the actual amount of growth, 

 secondly, by estimating the splitting of the proteins, as meas- 

 ured by the amount of amino nitrogen produced in the case of 

 proteins, or by the decreasing quantities of the amino nitrogen, 

 in the case of the amino acids, using the Van Slyke micro- 

 apparatus. 



No sweeping conclusions should be made from these experi- 

 ments as to the relative utilization of proteins and amino acids 

 by the different species of Actinomyces, because it is quite pos- 

 sible and even probable that different conditions, such as age of 

 culture, time since its isolation from a natural substratum, con- 

 centration of nitrogenous substances, nature of carbon com- 

 pounds, etc., may result in an entirely different range of figures; 

 but, even with all these limitations, certain definite conclusions 

 can be drawn. 



