GASTRIC CJECA OF THE HETEROPTERA. 15! 



author to the sterilization of the media at too high a temperature, 

 as it was found that the difference in rate of development largely 

 disappeared when the food was sterilized by the discontinuous 

 method at low temperatures. Maggots hatched from sterile 

 eggs were also treated with cultures of various bacteria, including 

 Bacillus coli, Bacillus proteus vulgaris, Bacillus putrificus, and 

 others, in order to determine the part taken by proteolytic 

 bacteria in development, as suggested by Bogdanow, but the 

 ^fected larvae developed no more rapidly than the sterile ones 

 and where Bacillus putrificus was used growth was clearly re- 

 tarded and the larvae died regularly before reaching the pupa 

 stage. Woolman concludes that: "Get example d'un etre qui, 

 a 1'etat naturel, semble vivre en association etroite avec les 

 bacteries, montre clairement que la vie animate est possible en 

 dehors de toute intervention des microorganismes." 



It can hardly be doubted that many insects, such as those 

 living parasitically in the body cavity of the host, normally 

 exist during the greater part of their life cycle in the total absence 

 of bacteria ; and according to Portier this is also true of the larvae 

 of certain leaf-mining microlepidoptera. This author found 

 that about 30 per cent, of the Lithocolletis larvae infesting oak, 

 elm, etc., were wholly free from bacteria and that practically 100 

 per cent, of the larvae of a species of Nepticula infesting the rose 

 and which do not void the excrement on the exterior of the mine 

 were also sterile. 



Notwithstanding the direct experimental evidence in support 

 of a digestive function for intestinal bacteria, as advanced by 

 Schottelius and others, the view appears to be generally held 

 by physiologists, largely on account of the characteristic limita- 

 tion of the different classes of intestinal bacteria to certain well- 

 defined regions of the digestive tract, that in the higher animals 

 at least, the actual solution of the nutrient materials in the food, 

 in the absorptive portion of the gut, is performed chiefly if not 

 entirely by the digestive secretion produced by the animal itself 

 and that the chief function of the "normal" intestinal bacteria 

 consists, not in any direct action on the food in preparing it for 

 resorption, but rather in preventing indirectly the undue multi- 

 plication of injurious forms which are continually invading the 

 intestine of the host. 



