14 



H. J. Sears 



the same number of organisms and kept for the full time of the experiment 

 under exactly the same conditions. When all but the control fiask had been 

 inoculated, they were sterilized by the addition of about 2% phenol. Two 

 cubic centimeters of N/1 HCl were added to each and the cultures filtered. The 

 filtrate, which was fairly clear, was made up to volume and aliquot parts taken 

 for the determinations. Table 3 gives the analytical results. As in Tables 1 

 and 2, the values are given in milligrams per 100 c.c. of the culture medium. 



TABLE 3 

 The Production or Amino-acid and Ammonia by Bacteria in a Peptone Solution 



A number of interesting facts are brought out by this experiment. In the 

 first place, the ammonia figures do not, in either case, indicate the relative ages 

 of the cultures. The 10-day culture of B. proteus, for example, shows a lower 

 concentration of ammonia nitrogen than the 8-day culture. Likewise, the 

 12-day culture of B. pyocyaneus contains a lower concentration of this compound 

 than the 9-day culture. Many other instances of the same irregularity may 

 be noted. It is apparent, therefore, that different cultures of the same organ- 

 ism on the same media and in exactly equal volumes may show quite different 

 rates of ammonia-formation, even when made and grown under exactly the 

 same conditions. In the case of both organisms, however, there is a general 

 increase' of ammonia-formation on the part of the older cultures up to the 

 15th or 16th day. After this the values fluctuate without any regular increase. 

 Evidently, in the volunxe of media used, these organisms reach their maximum 

 of ammonia-production in from about 14 to 18 days. 



