22 



"hormone" which can change the eye color from white to 

 "brown in Drosophila flies "being reared on tryptophane. 

 Neither the "bacteria nor tryptophane separately have any 

 influence on the production of eye pigment. In the 

 presence of "both the "bacteria and tryptophane , however, 

 eye pigmentation is greatly increased. According to Tatum, 

 this shows that tryptophane is able to modify eye -color 

 only through the intermediation of microorganisms. 



Bactericidal principle associated with ticks and in - 

 sects . Through the work of Hindle and Duncan (1925) and 

 Duncan (1926) it is known that certain arthropods possess 

 a "bactericidal principle in their alimentary tracts. 

 These workers found that while Bacillus anthracis , Bacillus 

 subtil is , and Streptococcus faecalis were able to survive 

 in the alimentary canal of the fowl tick, Argas persicus , 

 others, such as Staphylococcus aureus died quickly after 

 ingestion "by the tick and when tested in vitro the stomach 

 contents were found to "be definitely "bactericidal to 

 Staphylococcus aureus , Bacillus anthracis , and Bacillus 

 my co ides . The results with Pasteurella pestis and 

 Bacillus subtilis were inconclusive. Eberthella typhosa , 

 Serratia marcescens, Brucella abortus , and Streptococcus 

 faecalis were not affected. The inhibitory principle, 

 the potency of which varied with the individual tick, was 

 not inactivated "by exposure to a temperature of 58° C. for 

 thirty minutes. 



Duncan (1926) investigated further the nature of the 

 "bactericidal action and its occurrence or non-occurrence 

 in the following arthropods : Stomoxys calci trans , Musca 

 domestica , Anopheles bifurcatus , Aedes cinereus , Cimex 

 lectularius , Rhodnius prolixus , Argas persicus , and Orni- 

 thodoros moubata . He demonstrated a "bactericidal principle 

 in the gut contents of all of these, and with the exception 

 of the last two (ticks), in the feces as well. Staphylococci 

 and the spore -forming aerobes were the "bacteria most 

 affected "by this "bactericidal principle. These included 

 S t aphy lo co c cus aureus , Staphyloccus albus, Bacillus 

 anthracis , Bacillus subtilis , Bacillus me s enter i cus , and 

 Bacillus vulgatus . Also inhibited by the gut contents of 

 Argas persicus were Neisseria catarrhal is and Streptococcus 

 hemolyticus . Apparently there is only one active principle 

 in any given species of arthropod but different groups of 

 bacteria possess varying degrees of susceptibility to it. 

 The widest range of action, in Duncan's tests, was exhibited 

 by the gut contents of Argas persicus and Stomoxys calci - 

 trans and the narrowest by those of the bugs. The spore- 



