2 go 



THE SPOROZOA 



be swallowed by the new host with its food, in an accidental manner, 

 and pass into its alimentary canal ; then, and not till then, under 

 normal circumstances, does germination commence. Attempts to 

 produce infection by direct inoculation, by means of intermediate 

 hosts, or in other ways, were wholly unsuccessful. The first effect 

 of the action of the digestive juices is the extrusion of the filaments 

 of the polar capsules, which appear to act as organs of fixation, 

 attaching the spore to the epithelium of the digestive tract. The 

 two valves of the spore-membrane then separate along the suture 

 and permit the escape of the contained sporozoite, which emerges 

 as a minute amoebula and penetrates the wall of the digestive tract. 

 From this point the tiny parasite embarks upon migrations, in some 

 cases very extensive, in order to reach the organ or tissue which is 

 its final destination. It is not possible to state with any certainty 

 how these migrations are either effected or guided. In some cases 

 the journey is perhaps performed on foot, as it were, the little 

 amoeboid germ pushing its way actively through the tissues, like a 

 leucocyte. In other cases the parasite may be passively transported 

 by means of the blood-current. The latter method is probably the 

 more usual, the little germ being carried along suspended in the 

 blood-plasma ; at any rate, there is no evidence that it ever attacks 

 the blood-corpuscles. The one thing certain with regard to this 

 stage of the life-history is that the parasite is able to select and to 

 seek out, in some mysterious fashion, the specific organ or tissue 

 which it affects, and which may be situated at a considerable 

 distance from the original seat of infection. 



Finally, it should be noted that in Glugea bombycis of the silk- 

 worm disease, hereditary infection is effected by the penetration of 

 the parasite into the ovary and the formation of spores within the 

 ovum itself. Thus the newly -hatched silk- 

 worms are already infected with the disease 

 and disseminate it amongst healthy indi- 

 viduals. No other case of this kind is known 

 in the Myxosporidia, nor indeed in the whole 

 of the Sporozoa, with the possible exception 

 of the parasites of Texas-fever (p. 262). In 

 Glugea bombycis the infection of older cater- 

 pillars is effected exclusively by the accidental 



\ 



FIG. 100. 



Kidney-ceils of the carp ingestion of spores along with the food, so that 

 rfj^JffiSrtS^C here too casual infection is the normal type, 

 ra h idiy *myx The^fnyxJf supplemented by hereditary transmission of 



sporidian germs ; n, nuclei the disease-germs. 



of the kidney-cell. (After / \ a 7 j n/r 12- ? i- n 



Doflein.) (t) SCRUogOMf and Multiplicative Processes. 



When the amoebula reaches its definitive 



situation, it invades the tissues and commences to feed and to 



multiply endogenously with great activity. It is probable, how- 



