72 J. PERCY BAUMBERGER 



Nencki ('86) gave indirect evidence in this direction when he 

 showed that the action of digestive ferments on food-stuffs makes 

 them very quickly soluble and absorbable. The action of bac- 

 teria merely carries the decomposition to a lower level, yielding 

 unassimilable aromatic acids, fatty acids, phenol, kresol, indol, 

 skatol, carbon dioxide, methan, etc. The indications are, how- 

 ever, that microorganisms are of value as intestinal flora not 

 because of their digestive, but because of their synthetic power. 



MICROORGANISMS AS INTERNAL SYMBIONTS OF INSECTS 



In addition to the cases of internal symbiosis of fungi with 

 insects inhabiting dry wood, many Hemiptera and Blattidse are 

 also associated with microorganisms. These are usually bacteria 

 or yeasts and infest the ovary. For example, the pseudovitellus 

 of the aphid was long a puzzle to embryologists, but finally proved 

 to be a granular body containing yeast cells which in the further 

 development of the insect make complicated migrations and 

 finally become lodged in certain fat-bodies which are termed 

 mycetocytes or bacteriocytes, after which the infection of the 

 ovary takes place. The evidence that a real symbiotic relation- 

 ship exists in the Blattidse and Hemiptera is given by Buchner 

 and others as follows : 



1. All eggs are infected. 



2. The infection is not injurious to them. 



3. Each species of insect is associated with a definite species 

 of microorganism. 



4. This association is very definite and almost a specific 

 character. 



5. The yeasts profit by the relationship in the protection 

 which they receive from the host against the vicissitudes of the 

 environment. 



6. The yeasts multiply as the animal multiplies, always being 

 present in constant amount even in such rapidly increasing forms 

 as aphids and coccids. 



7. The yeasts and bacteria are of value to the host as destroyers 

 of waste products of metabolism, such as urates, according to 



