04 PARTICULAR CONSIDERATIONS ON THE 



quantity of water is very small, and the organic mattei 

 abundant, the production is usually of a vegetable nature; 

 when there is much water, animalcules are more frequent- 

 ly produced." It has been shown by the opponents ol 

 this theory, that when a vegetable infusion is debarred 

 from the contact of the atmosphere, by being closely seal- 

 ed up or covered with a layer of oil, no animalcules are 

 produced; but it has been said, on the other hand, that 

 the exclusion of the air may prevent some simple condi- 

 tion necessary for the aboriginal development of life — and 

 nothing is more likely. Perhaps the prevailing doctrine 

 is in nothing placed in greater difficulties than it is with 

 regard to the entozoa, or creatures which live within the 

 bodies of others. These creatures do, and apparently can, 

 live nowhere else than in the interior of other living ta>- 

 ^lies, where they generally take up their abode in the vro- 

 cera, but also sometimes in the chambers of the eye, the 

 interior of the brain, the serous sacs, and other places 

 having no communication from without. Some are vivi- 

 parous, others oviparous. Of the latter it cannot reason- 

 ably be supposed that the ova ever pass through the me- 

 dium of the air, or through the blood-vessels, for they are 

 too heavy for the one transit, and too large for the other. 

 Of the former, it cannot be conceived how they pass into 

 young animals — certainly not by communication from the 

 parent, for it has often been found that entozoa do not ap- 

 pear in certain generations, and some of peculiar and noted 

 character have only appeared at rare intervals, and in 

 very extraordinary circumstances. A candid view of the 

 less popular doctrine, as to the origin of this humble form 

 of life, is taken by a distinguished living naturalist. 6i To 

 explain the beginning of these worms within the human 

 body, on the common doctrine that all created beings pro- 

 ceed from their likes, or a primordial egg, is so difficult, 

 that the moderns have been driven to speculate, as our 

 fathers did, on their spontaneous birth ; but they have re- 

 ceived the hypothesis with some modification. Thus it 

 is not from putrefaction or fermentation that the entozoa 

 are born, for both of these processes are rather fatal to 

 their existence, but from the aggregation and fit apposi- 

 tion of matter which is already organized, or has been 

 thrown from organized surfaces. * * Their origin in 

 this manner is not more wonderful or more inexplicable 

 than that of many of the inferior animals from sections of 



