TRANSMISSION OF SARCOCYSTIS. 59 



about 0' 014 mm. long and 0*003 mm. broad. Tliese measurements 

 are probably the same for the spores of S. bubali. 



The spore is rounded at one end and pointed at the other. A 

 large nucleus containing a central deeply staining body, the karyo- 

 some, is present near the rounded end, while the faint striations 

 at the pointed end mark the position of a body which is possibly 

 identical with the polar capsule found among the Myxosporidia. 

 It is these structures which presumably carry the infection. Now 

 these spores possess no firm outer investment, which in the case of 

 the closely allied Myxosporidia is exceedingly well developed and 

 resistent. In fact it seems impossible to avoid the conclusion to 

 which such authorities as Wasielewski and Laveran and Mesnil 

 have come, that there must be an intermediate host conveying the 

 parasite from vertebrate to vertebrate. 



In the case of mice Smith* has shoAvn that murine caimibaUsm 

 may account for the conveyance, but such an explanation is im- 

 possible in the case of herbivorous forms, such as sheep and buffaloes. 

 Might not, however, some such insect as the blow-fly be the carrier ? 

 The blow-fly lays its eggs upon meat, and the larva, which feeds 

 upon the flesh, would, if it were infected with Sarcocystis, take the 

 spores into its gut, where it is conceivable that their further develop- 

 ment might result in the production of resistent cysts. These cysts 

 might persist inside the larva through the metamorphosis and 

 then gain access to the alimentary canal of the vertebrate host, 

 either by the adult blow-fly being swallowed alive, an untimely fate 

 which must not seldom overtake unwary individuals, or by the 

 decomposition of dead blow-flies upon the grass. It is also possible 

 that the adult blow-fly may transmit the infection direct by feeding 

 upon infected carrion or upon open sores of the living animal dis- 

 playing the cysts. That infection of the vertebrate host probably 

 takes place by the alimentary canal is indicated by the fact that the 

 most severely infected areas are always the oesophagus and trunk 

 muscles near the stomach. 



To test this hypothesis aU that is necessary is to shut up a number 

 of blow-flies in a wire cage with a small quantity of sugar for food 

 and a piece of freshly killed buffalo meat containing ripe cysts of 

 Sarcocystis. In a few houi's eggs are deposited upon the carrion, 

 and these in a warm atmosphere develop rapidly into fat, white 

 blow-fly larvae. After the larvae have fed for some time upon the 

 meat, the gut of the larva should be dissected out and examined 

 for spores of Sarcocystis or possible developmental forms. 



The method recommended for examining the gut contents is as 

 follows : The gut is cut out and slit open with a fine pair of scissors, 

 and the contents scraped out gently with a scalpel on to a coverslip. 

 The coverslip is then rapidly placed on a glass slide, and the edges 



* Theobald Smith. Jom-n. Exp. Med., Baltimore, VI., pp. 1-21. 



