METABOLISM OF ACTINOMYCETES 37 



did not change appreciably the reaction of the medium on ster- 

 ilization, thus eliminating the source of carbon as a factor in the 

 change in reaction (many nitrogen sources, namely the proteins 

 and amino acids, could also serve as sources of carbon). The 

 concentration of the sources of nitrogen in the experiment re- 

 ported in table 2 was as follows : all the inorganic nitrogen sources 

 0.2 per cent, organic substances (proteins, amino acids and 

 amides) 0.5 per cent. 



There were two periods of incubation of the cultures, the first 

 period for most organisms was fifteen to twenty days and the 

 second period thirty to thirty-five days; A. bovis and A. asteroides, 

 which are slower growing forms (at 25°) were incubated for thirty 

 and sixty days. The upper line (early) always designates the 

 earlier period of incubation, and lower line (late) the later period 

 of incubation for the same organism. 



The data given in table 2 clearly bring out the fact that the 

 change in reaction depends entirely upon the nitrogen source, 

 varying greatly in this respect with the different organisms. 

 Some of these data have been discussed in paper III of this 

 series, where the question of the utilization of different nitrogen 

 compounds by actinomycetes was taken up. It was pointed 

 out that certain compounds, such as leucin, seem to result, in 

 nearly all cases, in a more acid reaction and the possibility was 

 suggested that the change in reaction of a culture medium con- 

 taining proteins, as a result of the growth of microorganisms, may 

 be due to the fact that the particular organism may attack one 

 or another amino acid group in the protein molecule. 



The different species certainly do not behave alike in their 

 action upon the different sources of nitrogen. A. scabies, for 

 example, produced in nearly all cases, with different nitrogen 

 sources, a change in reaction towards alkalinity, having a larger 

 exponent, while A. asteroides, almost invariably, with few excep- 

 tions, changed the reaction towards acidity. The fact that the 

 organisms utilize the various amino acids in a different degree 

 may throw some light upon this question. But a great deal 

 more information on this subject is needed, before we can draw 

 any definite conclusions. 



