Ixxxiv REPORT 1870. 



more see again than a man can recall his infancy, I should expect to he a 

 •witness of the evolution of living protoplasm from not living matter. I 

 should expect to see it appear under forms of great simplicitj', endowed, like 

 existing Fungi, with the power of determining the formation of new pro- 

 toplasm from such matters as ammonium carbonates, oxalates and tartrates, 

 alkaline and earthy phosphates, and water, without the aid of light. That 

 is the expectation to which analogical reasoning leads me ; but I beg j-ou 

 once more to recollect that I have no right to call my opinion any thing but 

 an act of philosophical faith. 



So much for the history of the progress of Redi'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 Eedi, whether Xenogenesis 

 obtains, side by side with Homogencsis ; 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 offspriug 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 Yal- 

 lisnieri, Reaumur, and others, before the end of the first half of the eighteenth 

 century. The tapeworms, bladderworms, and flukes continued to be a strong- 

 hold 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 Sie- 

 bold, Yan Beneden, Leuckart, Kiichenmeister, and other helminthologists has 

 succeeded in tracing every such parasite, often through the strangest wander- 

 ings and metamorphoses, to an egg derived from a parent, actually or poten- 

 tially 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 develope into the original form. A polype may 

 give rise to Medusae, 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 species. 



But if we turn to pathology it offers us some remarkable approximations 

 to true Xenogenesis. 



As I have already mentioned, it has been known since the time of Vallisnicri 

 and of Reaumur, that galls in plants, and tumours in cattle, are caused by 

 insects, which lay their eggs in those parts of the animal or vegetable frame 

 of which these morbid structures are outgrowths. Again, it is a matter of 

 familiar experience to everybody that mere pressure on the skin will give rise 

 to a corn. Now the gall, the tumour, 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 noui-ishment which they receive to 

 their own pm-poses. 



Prom such innocent productions as corns and warts, there are all grada- 

 tions to the serious tumours which, by their mere size and the mechanical ob- 

 struction they cause, destroy the organism out of which they are developed ; 

 whUe, finally, in those terrible structures known as cancers, the abnormal 

 growtii has acquired powers of reproduction and multiplication, and is only 

 morphologically distinguishable from the parasitic worm, the life of which 

 is neither more, nor less, closely bound up with that of the infested organism. 



