302 ANNUAL OF SCIENTIFIC DISCOVERY. 



animals come from, if not spontaneously generated in the body? These 

 parasites are found in the blood, in the liver, in the brain, in the eye, nay, 

 even in the cxccs>ivdy minute egg itself. "How <jnt. they there? "is our nat- 

 ural question. This question, which is so easily answered on the supposition 

 that generation can take plaec spontaneously, presents the most serious diffi- 

 culties to science, because the massive weight of scientific evidence has been 

 year after year accumulating against such a supposition; until the majority 

 of physiologists have come to regard it as an axiom, that no generation 

 whatever can occur except by direct parentage. This axiom, which a small 

 minority has always rejected, has quite recently met with a formidable 

 questioner in M. Pouchet, the Avell-known physiologist of Rouen; and his 

 experiments and arguments having agitated the Academy of Sciences, our 

 readers may be interested if a review of the whole subject be laid before 

 them. 



The first person who assailed the notion of spontaneous generation was 

 K'.'di, the Italian naturalist, in his treatise " Experimenta circa Gcnerationem 

 rnsectorum," in which he reviewed the facts, and proved that the worms 

 and insects which appear in decaying substances, are really developed from 

 eggs deposited in those substances by the parents. So masterly was the 

 treatise, that no one since then has had the courage to maintain the produc- 

 tion of worms and insects spontaneously. It has been held as preposterous 

 to suppose that putrefaction could generate an insect as that it could gener- 

 ate a mouse which Cardan believed. Driven from the insect world, the 

 hypothesis has sought refuge in the world of animalcules and parasites ; and 

 there the hypothesis is not so easily defeated. Whoever turns over the pages 

 of Leeuwcnhoek, the first who extensively applied himself to microscopic 

 observations, will see that the Dutchman steadily set his face against spon- 

 taneous generation, because the microscope showed him that many even of 

 these minute animals had their eggs, and were generated like the larger ani- 

 mals. Since that time, thousands of observers have brought their contribu- 

 tions to the general stock, and each extension of our knowledge has had 

 the effect of narrowing the ground on which the " spontaneous " hypothesis 

 could possibly find footing; the modes of generation of plants and animals 

 are becoming more and more clearly traced ; and the necessity in each case 

 of a parent stock is becoming more and more absolute. It is true that there 

 are organic beings of which, as yet, Ave can only say that there is the strong- 

 est presumption against their being exceptions to the otherwise universal 

 rule of generation. We do not know, for example, how the Amelia arises; 

 no one has ever seen its eggs ; no one has ever seen its reproduction and, 

 what is more, it is perfectly easy to make them in any quantities. I have 

 done so repeatedly. Nevertheless, they can only be " made " under the con- 

 ditions which would be indispensable for their birth and development if they 

 were really generated from eggs ; and that they are so generated is a pre- 

 sumption which has every argument in its favor, except the direct evidence 

 of the eggs themselves. The question, then, comes to this : Is it more proba- 

 ble that a law of generation which is found to reach over the whole organic 

 world should have an exception, or that our researches have not yet been 

 able to detect the evidence which would bring this seeming exception also 

 under the law? One after the other, cases which seemed exceptions, have 

 turned out to be none at all; one after the other, the various obscuri- 

 ties have been cleared away, showing one law to be general; and it is there- 

 fore the dictate of philosophic caution which suggests that, so long as we 



