292 Account of a Filaria in a Horse's Eye. 



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 poivers, 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- 

 ena. 



Another theory has lately been advanced, which receives the 

 support of some highly respectable names in physiology. It is 

 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 is 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 to 

 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 

 better foundation to rest upon than Bremser's notion that intes- 

 tinal worms are formed by the presence of semi-assimilated nu- 

 tritious matter in the digestive tube. 



