40 



liquefaction of gelatin or coagulation of milk. These facts do not 

 support, then, Galeotti's second conclusion, that the conditions of 

 life which affect the chromogenic power are generally those which 

 have an unfavorable influence upon the bacteria themselves in all their 

 functions. 



d) The effect of light upon pigment production. 



Following the methods of Buchner and of Marshall Ward, 

 Dieudonn6 (13) confirmed the simpler experiments ofGaleotti (15) 

 regarding the effect of light upon bacterial chromogenesis. He used 

 B. prodigiosus and B. fluorescens, and found that the direct 

 sunlight of March, July, and August hindered development in 

 half an hour, while 48 hours of exposure entirely prevented pigmen- 

 tation and trimethylamine production. B. prodigiosus also lique- 

 fied gelatin more feebly. Eleven hours of incandescent electric light 

 killed both organisms. According to Dieud onus's investigations, 

 these effects were produced by the light and not by the heat rays, 

 the violet and ultra violet rays being the destructive agents, and the 

 red and yellow rays having no effect. The injury is chiefly to the 

 germs themselves, the chemical change produced in the medium being 

 a very small factor. Similar results were obtained with B. c o 1 i , 

 B. typhosus, and B. anthracis, confirming those of Ward, who, 

 however, limits the injurious effect to the violet end of the blue, the 

 actinic rays. 



Beck and Schultz (14) criticised Dieudonn6's methods, and 

 observed no injury to the development of B. prodigiosus, B. 

 pyocyaneus etc., from exposure to colored light, though in some 

 cases there was an influence upon chromogenesis (2 3 days). Diffuse 

 daylight was beneficial, darkness sometimes proving injurious, 

 (Staphyl. pyog. aureus and B. fluorescens). Direct sunlight 

 (3 days) produced colorless cultures. 



The results of Beck and Schultz do not seem very conclusive; 

 the non-effect of the colored light may have been due to the slight 

 intensity of the rays which passed through their light filters. In a 

 recent paper Oliver (17) used colored glass plates. 



A simple comparative study as to the effect of direct sunlight 

 upon a series of my organisms gave the following results. One loop- 

 ful-inoculations were made upon slant agar from 18 hour bouillon 

 cultures which had been grown in the dark ; these were used as 

 controls. The cloudy bouillon cultures were then exposed to the 

 March sunlight (according toDieudonnd as effective as that of 

 July), and similar agar slant cultures inoculated at intervals. These 

 agar cultures were then grown in the dark and examined after 24 hours, 

 48 hours, and ten days. The results are appended. 



