We have an excellent example of both of these kinds of motion in respiration. For the lungs, like the heart, are continually carried upwards and downwards by a natural movement, and are excited by any irritation to coughing and more frequent action; but they cannot form and regulate the voice, nor can singing be executed, without the assistance, and in some sort the command, of the sensorium commune.
But these matters will be more fully handled when we come to speak of the actions and uses of the brain, and to consider the vital principle or soul. So much we have thought fit to say by the way, that we might show the respect in which we hold our illustrious teachers, and our anxiety to carry them along with us in our labours.
EXERCISE THE FIFTY-EIGHTH.
Of the nutrition of the chick in ovo.
That the authority of the ancients is not to be rashly thrown off appears in this: it was formerly current doctrine, though many at the present day, Fabricius[302] among the number, reject it as a delusion and a foolish idea, that the embryo sucked in its mother’s womb. This idea nevertheless had Democritus, Epicurus, and Hippocrates for its supporters; and the father of physic contends for it on two principal grounds: “Unless the fœtus sucked,” he says,[303] “how should excrements be formed? or how should it know how to suck immediately after it is born?”
Now, whilst in other instances it is customary to swear by the bare statement of this ancient and most distinguished writer, his ipse dixit (ἀυτὸς ἔφη) sufficing, because he here makes an assertion contrary to the commonly received opinion, Fabricius not only denies the statement, but spurns the arguments in support of his conclusion. We, however, leave it to the judgment of skilful anatomists and learned physicians to say whether our observations on the generation of animals do not proclaim this opinion of Hippocrates to be not merely probable, but even necessary.
All admit that the fœtus in utero swims in the midst of an abundance of a watery fluid, which in our history of the egg we have spoken of as the colliquament, this fluid modern authorities regard as the sweat and excrement of the fœtus, and ascribe as its principal use the protection of the uterus against injury from the fœtus during any violent motion of the mother in running or leaping; and, on the other hand, the defence of the fœtus from injury through contact with neighbouring bones, or an external cause, particularly during the period when its limbs are still delicate and weak.
Fabricius[304] ascribes additional uses to this fluid, viz. “that it may moisten and lubricate all the parts around, and dispose the neck of the uterus to facile and speedy dilatation to the utmost extent; and all this is not less assisted by that thick, white, excrementitious matter of the third digestion, neglected by the ancients, which is unctuous and oily, and farther prevents the sweat, which may occasionally be secreted sharp and salt in quality, from excoriating the tender body of the fœtus.”
I readily acknowledge all the uses indicated, viz. that the tender fœtus may be secure against all sudden and violent movements of the mother, that he may ride safe in the “bat’s wings,” as they are called, and, surrounded with an abundance of water, that he may escape coming into contact with his mother’s sides, being restrained by the retinacular fluid on either hand: this circumambient fluid must certainly protect the body which floats in its middle from all external injury. But, as in many other instances, my observations compel me here to be of a different opinion from Fabricius. In the first place, I am by no means satisfied that this fluid is the sweat of the fœtus. And then I do not believe that the fluid serves those important purposes in parturition which he indicates; and much less that it is ever so sharp and saline that an unctuous covering was requisite to protect the fœtus from its erosive effects, particularly in those cases where there is already a thick covering of wool, or hair, or feathers. The fluid, in fact, has a pleasant taste, like that of watery milk, so that almost all viviparous animals lap it up, and cleanse their new-born progeny by licking them with their tongues, greedily swallowing the fluid, though none of them was ever seen to touch any of the excrements of their young.
Fabricius spoke of this fluid as saline and acrimonious, because he believed it to be sweat. But what inconvenience, I beseech you, were sweat to the chick, already covered with its feathers?—if indeed any one ever saw a chicken sweat. Nor do I think he could have said that the use of this fluid in the egg was, by its moistening and lubrifying qualities, to facilitate the birth of the chick; for the drier and older the shell of the egg, the more friable and fragile it becomes. Finally, were it the sweat of the embryo, or fœtus, it ought to be most abundant nearest the period of parturition: the larger the fœtus and the more food it consumes, the more sweat must it necessarily secrete. But shortly before the exclusion of the chick from the egg, namely, about the nineteenth or twentieth day, there is none of the fluid to be seen, because as the chick grows it is gradually taken up; so that if the thing be rightly viewed, the fluid in question ought rather to be regarded as nutriment than as excrement, particularly as he has said that the chick in the egg breathes, and lets its chirping be heard, which it certainly would not do were it surrounded with water.