GENERATION. 



467 



vagina of the bitch in such a way that none of 

 the fluid itself could escape, but only an 

 emanation, vapour, or supposed aura rising 

 from it, and in eighteen out of thirty animals 

 on which the experiment was performed, with 

 the subsequent occurrence of impregnation. 

 But until these experiments shall have been 

 confirmed by careful and frequent repetition, 

 we must be allowed to doubt the possibility of 

 performing such an experiment in a sufficiently 

 accurate manner. 



Spallanzani, with a view to investigate the 

 powers of a vapour supposed to rise from the 

 seminal fluid, exposed a quantity of the ripe 

 unimpregnated spawn of the frog for some 

 time in the same vessel with a quantity of 

 seminal fluid, the latter being placed at the 

 bottom of the vessel, the ova at the top, and 

 never was any fecundation produced ; an 

 experiment, it is true, from which no more 

 than negative evidence can be derived, but 

 upon the whole more worthy of trust as being 

 subject to fewer fallacies than those of Mondat. 

 The instances in which it has been alleged 

 that impregnation has taken place in the human 

 female without there being any possibility of 

 the seminal fluid itself passing inwards in the 

 female genital passages, are of a very doubtful 

 nature, and liable to so many sources of fallacy, 

 that we feel little disposed to admit them as 

 grounds of proof of the agency of an aura 

 seminalis. In some of the cases in which it 

 has been found, either in the course of pregnancy 

 or at the time of child-birth, that the female 

 passages are obstructed, there is reason to be- 

 lieve that the closure has been produced sub- 

 sequent to the occurrence of conception ; and 

 the same may be said of those cases of ovarian 

 gestations in which an obliteration of the Fal- 

 lopian tubes has been observed. In the greater 

 number of such cases, it may also be observed, 

 the malformation of the parts has consisted in 

 the much contracted state of the external orifice 

 or some other part of the passage, rather than 

 in their absolute closure, so that there was 

 merely a difficulty and not an impossibility of 

 the entrance of seminal fluid. But in opposi- 

 tion to such vague and ill-ascertained observa- 

 tions, a variety of circumstances, which it is 

 not necessary to particularize, might be adduced, 

 tending to show how very easily in the human 

 female as well as in other animals all mecha- 

 nical obstructions to the entrance of the seminal 

 fluid into the uterus tend to prevent conception. 

 General conclusions respecting fecundation. 

 In conclusion we would remark, 1st, that 

 while we readily admit a veiy small quantity 

 indeed of the seminal fluid to be sufficient to 

 produce fecundation, we think that what has 

 previously been stated warrants the conclusion, 

 that material contact of a certain quantity, 

 however small, of the seminal fluid with the 

 ovum is necessary to give rise to its fecunda- 

 tion, and, consequently, that the hypothesis 

 of an aura is untenable. And for the same 

 reasons it follows that there are no just grounds 

 for holding the opinion either that fecundation 

 consists in a sympathetic action of a nervous 

 kind, or that it is brought about by the absorp- 



tion of the semen into the circulatory or 

 lymphatic vessels of the generative system. 



2d. It is sufficiently obvious that in quadru- 

 peds there is no exact proportion between the 

 quantity of seminal substance or fluid received 

 by the female or emitted by the male, and its 

 effect in producing fecundation, a circum- 

 stance which points out a distinction which 

 ought always to be borne in mind between that 

 vital change on the female genital system and 

 the whole economy and ovum, and the simple 

 physical re-action which may take place be- 

 tween the semen and ovum themselves. 



3d. We may regard venereal excitement of 

 the genital organs and impregnation of an 

 ovum as different phenomena, for though they 

 usually occur together, there are instances in 

 which they take place quite independently. 



4th. The action of impregnation is to be 

 regarded as sui generis, or quite peculiar among 

 the vital processes. It is not capable of being 

 imitated by any other substance than the 

 seminal fluid, and neither experiment nor ob- 

 servation enables us to form the most distant 

 conjecture what the nature of that action may 

 be, which, from the influence of the male pro- 

 duct, confers upon the ovum a new and 

 independent life, and enables to give birth to 

 a new individual the mass of organic matter in 

 the egg, which, without the change of fecun- 

 dation, would prove altogether barren and 

 undergo no other changes than those of similar 

 dead matters. The action, however, is in some 

 respects reciprocal, and we cannot determine 

 what part either of the two agents concerned 

 performs in the change of fecundation : we 

 know only this, that unless the seminal fluid 

 be of the suitable composition it is ineffectual, 

 and that ova are susceptible of its influence 

 only when in that period of their evolution 

 when they are ripe. Nor can we with certainty 

 fix on what part of the egg the influence of the 

 male semen more immediately operates. Since 

 the foetus grows from the centre of the germinal 

 layer, it has been commonly supposed that 

 this is the part of the egg which is most imme- 

 diately affected by fecundation, but we know 

 nothing of this ; and it might be held, on the 

 other hand, that the effect of fecundation ope- 

 rates on the rest of the contents of the egg 

 in enabling them to be assimilated round the 

 germinal centre or rallying point of the de- 

 velopment of the new being. 



5th. It has not yet been shewn that one 

 part of the seminal fluid is more necessary to 

 impregnation than another. The seminal 

 animalcules form a natural ingredient of the 

 fluid secreted in the testicle at the time when 

 it is excreted for the purposes of propagation ; 

 they appear to be invariably present, but addi- 

 tional experiments are still wanting to prove 

 them to be the active or essential agents of 

 fecundation, much more the rudiments of the 

 - new being within the ovum. 



6th. Like others of the operations of the 

 animal economy, the action of fecundation is 

 known principally in its effects; but it seems 

 to be a question worthy of investigation whe- 

 ther, in the phenomena exhibited during fecun- 



