DISEASES OF THE DIGESTIVE ORGANS. 219 



sdniissit n of this explanation be sufficient ; for many of tlie entozoa 

 are not propagated by eggs, but belong to the viviparous class, 

 60 that in regard to them the difficulty remains undiminished. 

 But granting the existence of ova without, and tlieir reception into 

 the body, it is still impossible to explain the development from 

 them of the animals found in the parenchyma, in the embryo, etc., 

 without, at the same time, admitting that the ova are not only 

 carried to these localities through the blood-vessels, but actually 

 pass tlirough the walls of the capillaries. Such an admission 

 would be a physiological absurdity; for the extreme vessels will 

 allow of the passage of a single blood-globule at a time, and no 

 more, and will not permit any denser fluid than the plasma of the 

 jlood to permeate their walls. How, then, could they afford a 

 passage in any manner to ova, the least of which is ten times an 

 large as a blood globule? 



If the hypothebis now presented is untenable, it only remain ^j 

 to adopt the alternative one, to-wit : that entozoa are generated or 

 created anew out of the materials or the products of the living 

 organism. It may be urged affirmatively, in support of this doc- 

 trine, that each organ possesses its own entozoa — the kidney, a 

 species different from those of the intestine, which are, again, un- 

 like the parasites of the liver. Even more: the several ])arts of 

 the same organ generate dissimilar animals. The small intestine 

 produces the round and the tape-worms ; the large intestine, the 

 two species of thread-worms. These facts seem to show that some 

 extremely local concurrence of circumstances is essential to tlip 

 production of the several entozoa. It may also be argued, and we 

 think the argument unanswerable, that if spermatic animalcules, 

 which exist in the testicle, are there spontaneously generated, no 

 violence is done to probability in supposing parasitic animals to 

 be produced in the same manner. It will hardly be denied that 

 spermatozoa are literally evolved from the constituents of the 

 semen ; but it is objected to the doctrine of spontaneous generation 

 that it is agaiast analogy, which every-where supports the famous 

 dogma, omne vivum ex ovo. This objection is a mere begging of 

 the qucvstion. The decision of the case in hand involves the truth 

 of the theory just quo(ed, and, as we believe, must be allowed to 

 show that this theory is not absolutely universal in its application. 

 Other facts, also, among which are the following, tend to invali- 

 date it. Nothing can be more certain than that all or^^anired 



