MICRO-ORGANISMS 247 



some way be able to fix atmospheric nitrogen or transform 

 carbohydrate into protein. This faculty would appear to reside, 

 however, in the Protozoa, and it may be pointed out that since 

 the latter multiply and die in thousands within their hosts their 

 remains alone might furnish the nitrogen required by the latter. 

 Cleveland did not investigate the constituents extracted from the 

 wood by the Protozoa and what substances, if any, are thereby 

 released as food for the termites are undetermined. In a recent, 

 and very extensive, memoir by Cleveland and his collaborators 

 (1934) a rich Protozoan fauna, akin to that found in termites, is 

 described from the gut of the wingless, wood-feeding cockroach 

 Cryptocercus punctulatus of the United States. It was found that 

 the Protozoa of this insect contain the enzymes cellulase and 

 cellobiase, which produce dextrose in vitro. The cockroach, on 

 the other hand, does not possess cellulase, and probably not 

 cellobiase. It is, however, able to live longer without Protozoa 

 when dextrose is used as food, and it is concluded that this 

 carbohydrate is one of the important food constituents supplied 

 by the activities of the Protozoa. Trager (1932) has also 

 investigated the occurrence of cellulase in connection with the 

 above problem, and finds that it can be extracted from the Protozoa 

 living in the termite Termopsis, and also from those present in 

 Cryptocercus. In the defaunated hosts this enzyme was found 

 to be wanting. 



Apart from termites, most other wood-inhabiting insects 

 harbour micro-organisms of various types in the alimentary 

 canal, its appendages or other organs, and the subject is admirably 

 discussed by Buchner (1928). The actual nature of the food of 

 such insects is, in many cases, quite obscure, and it has been too 

 readily assumed that the wood-particles excavated during the 

 tunnelling process serve as food. The regular presence of micro- 

 organisms, generally in localised situations, lends indirect support 

 to the conclusion that the latter are symbionts which perform an 

 important digestive function. Thus Sitodrepa panicea, and many 

 other wood-boring beetles, possess special intestinal cgeca harbour- 

 ing yeast-like organisms. In the larva of the beetle Potosia 

 cuprea, which feeds upon dead pine needles, Werner (1926) has 



