292 Account of a Filaria in a Horse’s E’ye. 
opinion ; for it is not the obvious appearance of the organisms, 
whether vegetable or animal, that is disputed, but the cause of 
their appearance. A known organism appears in some unusual 
place from its previously known habitats, or an unknown one is 
observed in some locality never as yet minutely examined, or at 
least not made known that it has been examined ; the advocates 
of spontaneous generation immediately say, that our doctrine is 
the right one is plainly evident, because here an organism has 
appeared which cannot be accounted for otherwise. Is assertion 
to take the place of positive facts? and is not this mere assertion ? 
How can we prove that there were no germs of that type of or- 
ganisms in that place where we now observe the organism in 
question? We find, when we begin to examine it, that it pro- 
duces germs itself; then by what parity of reasoning can we 
assert that it has sprung from matter without any previous germ, 
when we find, in every succeeding instance, a germ is always 
given for a succeeding organism?” A full consideration of this 
subject would require an investigation into the nature. of the 
vital principle and the vital powers, which our limits will not al- 
low ; we therefore dismiss the question, with the single remark 
that it is more in accordance with the dictates of sound philoso- 
phy, in all doubtful cases, to acknowledge our ignorance than to 
attempt to assign a cause to explain such extraordinary phenom- 
-Another theory has lately been advanced, which receives the 
support of some highly respectable names in physiology. It 1s 
that worms are produced within the body by some living process 
or function of the organism, analogous to the secretion of lymph 
upon a serous surface. An organized portion of matter 1s thus 
formed, under the influence of the vital principle of the original 
animal, which is afterwards thrown off and becomes a separate 
being, and capable of an independent.existence.. In answer 10 
this hypothesis it is sufficient to say, that we have no proof what- 
ever of the existence of such formations; that they are contrary 
to all analogy, and will not explain the identity of characteristics 
which form the different genera and species. _In short, it has nO 
- foundation to rest upon than Bremser’s notion that intes- 
orms are formed by the presence of semi-assimilated DUr 
latter in the digestive tube. : 
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