258 ANNUAL OF SCIENTIFIC DISCOVERY, 



and tartrates, alkaline and earthy phosphates, and water, without 

 the aid of light. That is- the expectation to which analogical rea- 

 soning leads me ; but I beg you once more to recollect that I have 

 no right to call my opinion anything but an act of philosophical 

 faith. So much for the history of the progress of Recli's great 

 doctrine of biogenesis, which appears to me, with the limitations 

 I have expressed, to be victorious along the whole line at the 

 present day. As regards the second problem offered to us by 

 Redi, whether xenogenesis obtains, side by side with homogene- 

 sis; whether, that is, there exist not only the ordinary living 

 things, giving rise to offspring which run through the same cycle 

 as themselves, but also others, producing offspring which are of a 

 totally different character from themselves, the researches of two 

 centuries have led to a different result. That the grubs found in 

 galls are no product of the plants on which the galls grow, but 

 are the result of the introduction of the eggs of insects into the 

 substance of these plants, was made out by Vallisnieri, Reaumer, 

 and others, before the end of the first half of the eighteenth cen- 

 tury. The tape-worms, bladder-worms, and flukes continued to be 

 a stronghold of the advocates of xenogenesis for a much longer 

 period. Indeed, it is only within the last thirty years that the 

 splendid patience of Von Siebold, Van Beneden, Leuckart, Kiich- 

 enmeister, and other helminthologists, has succeeded in tracing 

 every such parasite, often through the strangest wanderings and 

 metamorphoses, to an egg derived from a parent, actually or 

 potentially like itself; and the tendency of inquiries elsewhere 

 has all been in the same direction. A plant may throw off bulbs, 

 but these, sooner or later, give rise to seeds .or spores, which 

 develop into the original form. A polype may give rise to 

 medusas, or a pluteus to an echinoderm, but the medusa and the 

 echinoderm give rise to eggs which produce polypes or plutei, 

 and they are therefore only stages in the cycle of life of the spe- 

 cies. But if we turn to pathology it offers us some remarkable 

 approximations to true xenogenesis. As I have already men- 

 tioned, it has been known since the time of Vallisnieri and of 

 Reaumur, that galls in plants, and tumors in cattle, are caused by 

 insects, which lay their eggs in those parts of the animal or vegeta- 

 ble frame of which these morbid structures are outgrowths. Again, 

 it is a matter of familiar experience to everybody that mere pres- 

 sure on the skin will give rise to a corn. Now the gall, the tu- 

 mor, and the corn are parts of the living body, which have 

 become, to a certain degree, independent and distinct organisms. 

 Under the influence of certain external conditions, elements of 

 the body, which should have developed in due subordination to its 

 general plan, set up for themselves and apply the nourishment 

 which they receive to their own purposes. From such innocent 

 productions as corns and warts, there are all gradations, to the 

 serious tumors which, by their mere size and the mechanical 

 obstruction they cause, destroy the organism out of which they 

 are developed ; while, finally, in those terrible structures known 

 as cancers, the abnormal growth has acquired powers of re- 

 production and multiplication, and is only morphologically 



