CHAP. IV.

 

Of the Generation of Animals.

 

As the organization of men, and of other animals, is the most perfect, and the most complex, the propagation of them is likewise most difficult, and the number of individuals is less abundant.  I except here such animals as can be multiplied by a separation of their parts, or without the aid of generation, these having been sufficiently treated of in the preceding chapter.*

 

But how will the theory delivered in the former chapter apply to the generation of men, and other animals, who are distinguished by sexes?  We understand, from what has been said, how every individual may reproduce; but we cannot conceive how two individuals, the one a male, and the other a female, should uniformly produce a third.

 

Before replying to this objection, I must observe, that the writers on this subject have confined their ideas solely to the generation of men and of animals, without attending to the nature [49] of reproduction in general:  And, as the generation of animals is the most complicated species of reproduction, they have laboured under great disadvantages, not only by attacking the most difficult point, but by leaving themselves no subject of comparison to enable them to illustrate the question.  To this circumstance I chiefly attribute the unsuccessfulness of their attempts.  But, by the route I have taken, I am persuaded that I shall be able to give a satisfactory explanation of every species of reproduction.

 

Let the generation of man serve as an example.  To begin with infancy:

 

The expansion and growth of the different parts of man’s body being effected by the intimate penetration of organic particles analagous [sic] to each of these parts, all the organic particles, in early life, are absorbed, and entirely employed in unfolding and augmenting his different members.  He has, of course, little or no superfluous particles, till his growth be completed.  It is for this reason that infants are incapable of propagating.  But, when his body has nearly attained its full size, he requires not the same quantity of organic particles; the surplus is, therefore, sent from all parts into reservoirs destined for their reception.  These reservoirs are the testes and seminal vessels.  At this very period, when the growth of the body is nearly finished, puberty commences, and every phaenomenon attending it discovers a superabundance [50] of nourishment:  The voice changes into a deeper tone; the beard begins to appear, and other parts of the body are covered with hair; the parts destined for generation are suddenly expanded; the seminal fluid fills the reservoirs prepared for its reception; and, without provocation, it escapes from the body during sleep.  This superabundance is still more evident in the female:  It discovers itself by a periodic evacuation, which begins and terminates with the faculty of propagating; by a quick increase of the breasts; and by a change in the sexual parts, which shall be afterwards explained.*

 

I conceive, then, that the organic particles sent from all parts of the body into the testicles and seminal vessels of the male, and into the ovarium of the female, compose the seminal fluid, which, in either sex, as formerly observed, is a kind of extract from the several parts of the body. These organic particles, instead of uniting and forming an individual similar to that in whose body they are contained, as happens in vegetables, and some imperfect animals, cannot accomplish this end without a mixture of the fluids of both sexes. When this mixture is made, if the organic particles of the male exceed those of the female, the result is a male; and, if those of the female most abound, a female is generated. I mean not that the organic particles of the male or of the female could singly produce [51] individuals: A concurrence or union of both is requisite to accomplish this end. Those small moving bodies, called spermatic animals, which, by the assistance of the microscope, are seen in the seminal fluids of all male animals, are, perhaps, organized substances proceeding from the individual which contains them; but, of themselves, they are incapable of expansion, or of becoming animals similar to those in whom the exist. We shall afterwards demonstrate, that there are similar animalcules in the seminal fluids of females, and point out the place where this fluid is to be found.

 

It is probable, that these organic bodies are only the first rudiments of an animal, containing nothing but its essential parts. We shall not enter into a detail of proofs on this subject, but content ourselves with remarking, that the organization of these pretended spermatic animals may be very imperfect; or rather, that they have the living organic particles mentioned above, which are common both to vegetables and to animals; or, at most, that they are only the first junction of these particles.

 

But, to return to our subject. It may be asked, how is it possible that the superfluous organic particles should be detached from all parts of the body, and unite upon the mixture of the male and female fluids? Besides, are we certain that such a mixture takes place?  Has it not been mentioned, that the female furnishes no fluid of [52] this kind?  Is it an established fact, that the male fluid enters the uterus? &c.

 

To the first question I reply, that, if what I had said concerning the penetration of the internal mould by the organic particles, in growth and nutrition, had been properly understood, it would be easy to conceive, that, when these particles are unable to penetrate the parts into which they formerly entered, they must take another rout, and, of course, arrive at some other part, as the testicles and seminal vessels.  Every attempt to explain the animal oeconomy, and the various motions of the human body, by mechanical principles alone, must be vain and ineffectual; for it is evident, that the circulation of the blood, muscular motion, and other functions of an animated body, cannot be accounted for by impulsion, or by any of the common laws of mechanism.  It is equally evident, that growth and reproduction are effects of laws of a different nature.  Why, then, do we refuse the existence of penetrating forces which act upon the whole substances of bodies, when we have examples of such powers in gravity, in magnetic attraction, in chemical affinities?  Since, therefore, we are assured by facts, and by a number of constant and uniform observations, that there are powers in nature which act not by impulsion, why are not these powers ranked among mechanical principles?  Why do we reject them in the explanation of effects [53] which they are known to produce? Why are we desirous of employing only the power of impulsion?  Is not this equally absurd as to judge of painting by the touch; to explain the phaenomena that belong to the mass by those that relate, only to the surface; or to use one sense in place of another?  It is limiting the reasoning faculty to a small number of mechanical principles, which are by no means sufficient to explain the various effects of nature.

 

But, if these penetrating forces be once admitted, is it not natural to imagine, that those particles which are most analogous to one another will unite in the most intimate manner; that each part of the body will appropriate those which are most agreeable to its nature; and that the whole superflouous particles will form a seminal fluid, which shall contain all the organic particles necessary for forming a small organized body, similar in every respect to that from which the fluid is extracted?  May not a force, similar to that which is the cause of growth, be sufficient to collect the superfluous organic particles, and bestow on them the figure of the body from which they proceed?

 

That our food contains an immense number of organic particles, requires no formal proof; since we are solely nourished by animals and vegetables, which are organized substances.  In the stomach and intestines, the gross parts of the aliment are separated and rejected by the excre- [54] tories.  The chyle [sic], which is a purer part of the aliment, is absorbed by the lacteal vessels; from thence it is carried into the mass of blood, and, in the course of circulation, it is more and more refined, the unorganic and useless particles being thrown out by transpiration and other secretions:  But the organic particles are retained, because they are analogous to the blood, and are attracted by it.  Hence, as the whole mass of blood passes several times through the body, during the course of this perpetual circulation, I suppose, that each particular part attracts those particles which are most analagous [sic] and allows the rest to move on.  In this manner all the parts are nourished and unfolded, not, as is commonly imagined, by a simple addition of matter to their surfaces, but by an intimate penetration of substance, effected by a force which acts equally upon every point of the whole mass:  And, after the different parts have acquired their utmost growth, and are fully impregnated with similar organic particles, as their substance becomes then more dense and solid, I imagine that they lose their faculty of attracting and receiving the particles presented to them.  But, as the particles continue to be carried round in the course of the circulation, and are no longer absorbed in such quantities as formerly, they must, of necessity, be deposited in some particular reservoir, such as the testicles and seminal vessels.  When this fluid extract of the male is mixed [55] with that of the female, the particles which are most analogous to each other, being actuated by a penetrating force, unite and form a small organized body, similar to the one or the other sex; and this body, when once formed, requires only an expansion of its parts, an operation which is performed in the womb of the mother.

 

We shall now consider the second question, namely, whether the female has a seminal fluid similar to that of the male?  In the first place, though such a fluid exists in females, the mode of emission is very different from that of the male, being generally confined within the body.*  The antients were so cofidnet of the existence of a female fluid, that they distinguished the two sexes by their different modes of emission.  But those physicians who attempt to explain generation by eggs, or by spermatic animalcules, insist, that females have no peculiar fluid; that the mucus issuing from the parts has been mistaken for a seminal fluid; and that the opinion of the antients on this subject is destitute of foundation.  This fluid, however, does exist; and the doubts concerning it have arisen solely from the attachment to systems, and from the difficulty of discovering its reservoir. The fluid which is separated from the glands about the neck and orifice of the uterus, has no visible reservoir; and, as it flows out of the body, it is natural to think that it is [56] not the prolific fluid, because it cannot co-operate in the formation of the foetus, which is performed within the uterus.  The reservoir for the prolific fluid of the female, therefore, must be situated in a different part:  it even flows abundantly; though, like that of the male, a small quantity is sufficient to produce a foetus.  If a little of the male fluid enters the uterus, either by its orifice or by absorption, and meets with the smallest drop of the female fluid, it is sufficient for the purpose of propagation.  Thus, neither the observations of some anatomists, who maintain that the seminal fluid of the male can have no admission into the uterus, nor the opposite opinion maintained by their antagonists, have any influence upon the theory we are endeavouring to establish.  But the discussion of these points we leave to a future opportunity.

 

Having obviated such objections as might be made, let us attend to the evidences that concur in supporting our hypothesis.  The first arises from the analogy between growth and reproduction.  It is impossible to give a satisfactory account of growth or expansion, without having recourse to those penetrating forces, those affinities or attractions which we employed in explaining the formation of the small organic bodies that are similar to the large bodies which contain them.  A second analogy is derived from this circumstance, that both nutrition and reproduction proceed, not only from the same effi [57] cient, but from the same material cause, namely, the organic particles of food; and what proves the surplus of the nutritive particles to be the cause of reproduction, is, that the body is not in a condition to propagate till its growth be finished:  Of this we have daily examples, in dogs and other animals, who follow, more closely than we do, the laws of nature:  They have no inclination to propagate till they have nearly attained their full growth; and by this we know whether the growth of a dog be finished; for he seldom grows after being in a condition to generate.

 

Another proof that the seminal fluid is formed of the surplus of nutritive particles, arises from the condition of eunuchs and other mutilated animals:  In this unnatural state, animals grow fatter than those who retain all their parts.  The superabundance of nutriment, having no organs for its evacuation, changes the whole habit of their bodies.  The knees and haunches of eunuchs grow uncommonly large.  The reason is evident.  After their bodies have acquired the common size, if the superfluous organic particles found an issue, as in other men, the growth would proceed no farther.  But, as they want organs for emitting the seminal fluid, which is nothing but the superfluous nutritive particles it remains in the body, and has a constant tendency to expand the parts beyond their natural size.  Now, bones, it is well known, grow or [58] extend by their extremities, which are soft and spongy, and, when they have once acquired solidity, they are incapable of farther extension:  Hence the superfluous organic particles can only enlarge the spongy extremities of bones; and this is the reason why the haunches, knees, &c. of eunuchs augment to a disproportioned bulk.

 

But the strongest proof of the truth of our present doctrine arises fro the resemblance of children to their parents.  Sons, in general, resemble their father more than their mothers, and daughters have a greater resemblance to their mothers than their fathers; because, with regard to the general habit of a body, man resembles a man more than a woman, and a woman resembles a woman more than a man.  But, as to particular features or habits, children sometimes resemble the father, sometimes the mother, and sometimes both.  A child, for example, will have the eyes of the father, and the mouth of the mother, or the colour of the mother and the stature of the father. Of such phaenomena it is impossible to give any explication, unless we admit that both parents have contributed to the formation of the child, and, consequently, that there has been a misture of two seminal fluids.

 

These resembles long embarrassed me, and, till I had maturely considered the subject of generation, led me into many errors and prejudices:  And is was not without much thought, a minute [59] examination of a great number of families, and a multiplicity of evidence, that I could prevail on myself to alter my former opinion, and to embrace what I now believe to be truth.  But the objections which might occur concerning mulattoes, mongrels, mules, and particular parental resemblances, instead of opposing my theory, I despair not of being able to show that they strengthen and confirm it.

 

In outh, the seminal fluid is less copious, but more stimulating.  Its quantity continues to augment till a certain age; because, in proportion as we approach that age, the parts of the body become more solid, admit fewer nutritive particles, send back more of them to the common reservoirs, and, of course, augment the quantity of the seminal fluid.  Thus, if the external organs have not been used, middle-aged men, or even old men, procreate with more ease than young men.  This is evidently the case with the vegetable tribes:  A tree, the older it is, produces the greater quantity of fruit.

 

Young people, who, by forced irritations, determine an unnatural quantity of this fluid into the reservoirs prepared for its reception, immediately cease to grow, lose their flesh, and at last fall into consumptions.  The reason is apparent:  They lose, by premature and too frequent evacuation, the very substance which nature intended for the nourishment and growth of their bodies.  [60]

 

Men who are thin, but not emaciated, and those who are plump, but not fat, are the most vigorous.  Whenever the superabundant nutritive particles begin to form fat, it is always at the expence of the seminal fluid and other generative powers. When the growth of the different parts of the body is compleat, when the bones have acquired full solidity, when the cartilages begin to ossify, and, lastly, when the parts almost refuse the admission of nutritive particles, then the fat augments considerably, and the quantity of seminal fluid diminishes; because the nutritive particles, instead of being sent back to the reservoirs, are arrested in every part of the body.

 

The quantity of seminal fluid not only increases till we arrive at a certain age, but it becomes more thick.  It contains, in the same bounds, a greater quantity of matter.  Its specific gravity is nearly double that of the blood; and, of course, it is heavier than any other animal fluid.

 

To a man in health, an evacuation of this fluid whets the appetite:  He soon finds the necessity of repairing the loss by fresh nourishment.  Hence we may conclude, that abstinence and hunger are the most effectual checks to luxury of every kind.

 

Many other remarks might be made on this subject, which must b e deferred till we come to treat of the history of man:  We shall, therefore, [61] conclude with a few observations.  Most animals discover no inclination for the sexes till their growth be nearly finished:  Those which have but one season in the year, have no seminal fluid excepting at that time.  Mr Needham* not only saw this liquor forming in the milt [sic] of the Calmar, but likewise the spermatic animals, and the milt itself, which have no existence till the month of October, when this fish spawns on the coasts of Portugal, where Needham nade the observation.  After the spawning time is over, the seminal liquor, the spermatic animals, and the milt, dry up and totally disappear; till the same season returns next year, when the superfluous nutritive particles renew the milt as formerly.  The history of the deer will be furnish us with an opportunity of remarking the various effects of rutting, the most conspicuous of which is the extenuation of the animal; and, in those species of animals whose rutting or spawning happens but once in a year, the extenuation of their bodies is proportionally great.

 

As women are smaller and weaker than men, as their constitutions are more delicate, and, as they take less food, it is natural to think that their superfluous organic particles should also be less abundant:  Of course, their seminal fluid will be weaker and smaller in quantity than that of men; and, since the fluid contains fewer organic particles, must not a greater num- [62] ber of males than of females result from a mixture of these two fluids?  This is really the case; and to account for it has hitherto been deemed impossible.  The number of males born exceeds that of females about a sixteenth part; and we shall afterwards see that the same effect is produced by the same cause in all the different species of animals.

Notes

 

* Here the Author gives an unnecessary recapitulation of Chap. III. To which the reader is referred [Smellie’s note; back to page 49].

 

* See below the Nat. Hist. of Man, chap. 2 [Smellie’s note; back to page 51].

 

* Quod intra se semen jacit, soemina vocatur; quod in hae jacit, mas; Aristot. De animalibus, art. 18 [back to page 56].

 

* See Needh. New miscroscopical discoveries, London 1745 [back to page 62]