30 L. F. RETTGER, N. BERMAN AND W. S. STURGES 



proteins, when added to the bacterial suspensions after periods 

 of preUminary incubation, remained unaffected. In every in- 

 stance where the test was satisfactorily carried out the quality 

 and degree of color obtained in the biuret test remained un- 

 changed, as is readily seen by comparisons with the controls 

 or with the standard peptone solution. 



Autolysis of the bacterial cells was always accompanied by a 

 change in the staining properties of the individual organisms. 

 In many cases, as for example in the complete autolysis of B. 

 subtilis material, the bacilli took on only a faint color; and the 

 presence of numerous fine granules presented a picture far from 

 the normal. A difference in staining properties was also occa- 

 sionally observed in the organisms of the B. coli type, but this 

 was never marked, and was not due to actual destruction of the 

 cell protein, as was shown always by the biuret test. The change 

 was due to some process other than autolysis, as for instance 

 "washing" or "laking" of the bacterial cells. 



GENERAL DISCUSSION AND CONCLUSIONS 



The results of the present investigation strongly indicate that 

 bacteria are unable to attack and bring about the decomposition 

 of proteins without the aid of enzymes or other proteolytic agents. 

 This applies not only to the more complex proteins like egg 

 albumin, but in all probability to albumoses and peptones as 

 well. Coagulated albumin shows the same resistance to the 

 direct action of bacteria of both the gelatin-liquefying and non- 

 liquefying types as the unheated and unchanged native proteins. 



By means of the quantitative biuret test of Vernon the dis- 

 appearance of proteoses and peptones from solutions serving as 

 test or culture media may be readily demonstrated. This method 

 has been of much value to us in the present investigation. It is 

 being employed for the determination of other proteins also, as 

 for instance casein in the form of nutrose. 



Even during prolonged incubation of flasks containing the 

 necessary inorganic salts for bacterial metabolism, together with 

 proteoses or Witte's peptone, little if any loss of these soluble 



