86 FRED W. TANNER 



Forty-two strains were able to decompose casein. This 

 reaction, of course, was more marked with a few of the forms 

 than with the majority. 



Temperature relations 



The temperature relations of any group of bacteria are very 

 important. It is often believed that since an organism is found in 

 nature outside the body, it has its optimum temperature and 

 grows best at temperatures near 20 °C., and that growth is 

 restricted at 37°. The literature on fluorescent bacteria indicates 

 that very few of these forms refuse to grow at 37°. All the 

 cultures used in this study were found to grow well at this tem- 

 perature. The amount of change brought about by bacteria 

 may be said, generally speaking, to be a function of the incuba- 

 tion temperature and period of incubation, in accordance with 

 the laws which govern enzyme action and the relation of tem- 

 perature thereto. 



Fluorescence 



This characteristic was a necessary requisite for the inclusion 

 of a culture in the investigation. It is closely related to the 

 pigment which these bacteria form. Some bacteriologists have 

 attempted to separate B. pyocyaneus and B. fluorescens-lique- 

 faciens on the ground that B. pyocyaneus possessed no fluo- 

 rescent pigment. This separation is probably more apparent 

 than real. There were all gradations among the cultures of 

 this series with regard to this characteristic. The forms which 

 liquefied gelatin and casein produced more fluorescent pigment 

 than those which did not break up these two compounds. 



Color in nature 



The theories with regard to color or pigment formation are 

 reviewed by Sullivan (1905). He divides pigments into two 

 divisions, viz: structural and pigmental. Pigments in nature 

 are divided into: (a) Pigments of direct importance, as in 

 respiration; (b) derivatives of such pigments; (c) waste products, 



