SPONTANEOUS CONGESTION AND INFECTIOUS DISEASES. 759 
not, some day, be artificially brought together. All I feel justified in 
affirming is, that I see no reason for believing that the feat has been 
performed yet. And, looking back through the prodigious vista of the 
past, I find no record of the commencement of life, and therefore I am 
devoid of any means of forming a definite conclusion as to the conditions 
of its appearance. Belief, in the scientific sense of the word, is a serious 
matter, and needs strong foundations. To say, therefore, in the admitted 
absence of evidence, that I have any belief as to the mode in which the 
existing forms of life have originated, would be using words in a wrong 
sense. But expectation is permissible where belief is not ; and if it were 
given me to look beyond the abyss of geologically recorded time to the still 
more remote period when the earth was passing through physical and 
chemical conditions which it can no more see again than a man can recall 
his infancy, I should expect to be a witness of the evolution of living 
protoplasm from not living matter. I should expect to see it appear under 
forms of great simplicity, endowed, like existing Fungi, with the power of 
determining the formation of new protoplasm from such matters as am- 
monium 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 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 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 Redi, whether Xenogenesis obtains, side by 
side with Homogenesis ; 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 
Yallisnieri, Reaumur, and others, before the end of the first half of the 
eighteenth century. The tapeworms, bladderworms. 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 Yon Siebold, Yan Beneden, Leuckart, Kuchenmeister, 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. 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 Medusse 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 Yallisnieri and of Reaumur, that galls in 
plants, and “ warbles ” of 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 “warble,” 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 
