ANIMAL PARASITES. 5 



active migration without some irritation of the regions of the 

 body through which they pass, whether this migration is per- 

 formed by the youngest brood, which is the usual course, or by 

 the mature or nearly mature animal, which takes place but 

 rarely, and that amongst the Nematoidea. Nature, with rare 

 exceptions, endeavours to render those immature grades of 

 development, which are passed through by these animals out of 

 the intestinal canal, innocuous, by the process of encysting, and 

 in these stages symptoms of pressure especially prevail. The passive 

 migration, however, of all still-immature parasites into the human 

 intestine takes place without any perceptible morbid symptoms. 



The general jjrognosis follows naturally from the observations 

 just recorded, and it is easily seen that the most dangerous indi- 

 viduals for the moment are the young animals engaged in their 

 migration. Next to these the migrating, mature individuals, 

 which inhabit the intestinal canal, produce the most dangerous 

 symptoms. The encysted states, or those in which the 

 animals reside in closed cavities, can only become dangerous to 

 life by their presence when they attain an enormous size, but 

 when smaller may be present without doing any mischief. 

 Lastlv, most of the mature individuals are more accessible to 

 curative processes than those of the lower stages, which live out- 

 side the intestinal canal. 



The general therapeutics will have to keep a double object in 

 view : 



1. The removal and destruction of the mature individuals with 

 their progeny. 



2. The observation of the mode of life and migration of the 

 immature individuals $ and, in places where such plagues are 

 endemic, of the habits and mode of life of the people, which 

 facilitate this migration— so as to found a rational prophylaxy 

 upon these observations. 



First Class — Infusoria. 



As the Vibriones (PI. I, fig. 1) and their allies, such as Bur- 

 sari®, Monades, and Bodones, are a peculiar attribute of fer- 

 menting and putrefying fetid animal substances, or always pre- 

 suppose a half-dead soil, and do not derive their nourishment so 

 much from living substances as from matters which the living 



