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enjoys in some form or other an existence external to the bodies of 

 animals, is derived, as I think, from the circumstance already men- 

 tioned as having been observed with respect to its limited local dis- 

 tribution, even in those regions where it is endemic. It has been 

 stated by various writers, and I have had the observation confirmed 

 by men who had been on the coast of Africa, that the prevalence of 

 the Guinea worm is sometimes defined by a distance of a few leagues. 

 That in one part, for instance, of the coast, almost every inhabitant 

 will be found affected with it, whilst at another, only a few leagues 

 off', the worm will be almost unknown, notwithstanding there being 

 no restriction upon the intercourse between the inhabitants of the 

 one part with those of the other. It may also be observed that the 

 Guinea worm is never found to spread from one person to another in 

 any other parts of the world than those indicated above, or as it may 

 be said, where it is indigenous, even allowing that the contagion is 

 direct from person to person, even there. The island of Curacoa af- 

 fords, as has been already mentioned, the only doubtful exception to 

 this position. 



Now I think that consideration of these facts will lead to the pro- 

 bable supposition that the worm requires, in some stage of its exis- 

 tence, a certain condition of external nature for its propagation and 

 development. For it is evident that during its latent stage it must 

 be, to a great extent, independent of external influences, and will 

 arrive at maturity as a parasite under the most various conditions of 

 climate and race in the person affected with it. 



The conclusions, then, to which I am inclined to come from what 

 is known respecting the Guinea worm, are : — 



1. That the parasitic condition is one phase or stage of its life, 

 not as an individual, but as a species. 



2. That this parasitic form is preceded and followed by other 

 forms, in one of which the species exhibits itself in its complete 

 development, and is probably like other worms of the nematoid class 

 — bisexual ; and that the young found within the parasitic form 

 represent probably these complete individuals in the embryo state. 



3. That these embryos arrive at their full development externally 

 to the animal economy, and require for their development conditions 

 of external nature which appear to occur only in some parts of the 

 globe. 



4. That the perfect form of the Filaria medinensis is at present 

 unknown, and is to be sought for, in all probability, only in those 

 countries where the worm is endemic as a parasite. 



