MICROSPORIDIA 339 



7) Problems concerning infection through the digestive tract. 

 The fact that the silkworm larva becomes infected by Nosema 

 boinbycis through ingestion of spores has been repeatedly proved. 

 Fantham and Porter w^ere able to infect the honey-bee by feeding 

 it on honey to which spores of Nosema apis were added. Weissen- 

 berg (1913, 1921) succeeded in obtaining positive experimental 

 infections with Glugea anomala. The writer also succeeded in in- 

 fecting the larvae of Cnlex territans with the spores of Stempellia 

 magna (Kudo, 1925). 



On the other hand, a number of investigators obtained negative 

 results by carrying out experimental infections. Henneguy and 

 Thelohan (1892) failed to obtain positive results by feeding the 

 host crustaceans with Thelohania giardi and T. octospora. Henne- 

 guy thought that the infection probably does not take place through 

 the digestive tract in view of the fact that lesions are found at 

 first at places remote from the alimentary canal. A somewhat 

 similar case was recently noted by Mattes (1928). Goodrich 

 (1920) kept under observation a prawn infected by T. octospora 

 in an aquarium with normal prawns and other crustaceans, without 

 finding any infection among any of these crustaceans. Wenyon 

 (1926) tried without success artificial infection of Thelohania sp., 

 which had been discovered by MacGregor in the larvae of A'edes 

 nemorosiis and remarked that it seemed evident that infection de- 

 pends on certain conditions not at present known. 



Zwolfer (1926) likewise failed in bringing about infection in 

 Gammarus pulex by feeding with spores of Plistophora bloch- 

 manni taken from freshly killed host animal, although he noted 

 numerous empty spores in the host's gut lumen fifteen hours after 

 feeding and also numerous binucleate amoebulse which appeared 

 to have emerged from the spores. No stages of the parasite were, 

 however, found in the body cavity or muscles, although some ex- 

 perimental animals were kept as long as six weeks. Zwolfer could 

 not explain this failure, since the spores were apparently fully 

 mature as seen from the emergence of the amoebulse. Mattes (1928) 

 also obtained negative results by feeding normal host larvae 

 (Ephestia kuehniella) with Thelohania ephestice; the spores re- 

 covered from the fecal matter or the gut of the experimental larvae 

 did not show any noticeable changes. 



Why these failures? Does a spore have to pass through a long 

 resting period in order to become infective? Zwolfer thinks this 



