V. MISCELLANEOUS TOPICS RELATING TO TIM PRECEDING HISTORY OF GENERATION.
We have deferred until now the consideration of some topics which usually find a place in the history of the generative function, as we have thought it desirable to separate them from the preceding narrative on account of the vagueness of the facts and speculative nature of the opinions with which they are connected. The subject last discussed naturally leads to the first of these topics which we shall con sider, viz.
§ 1. Superfatation.—In the first section of Part IV. it has been mentioned that in the human female, as soon as the ovum has arrived in the uterus, and even a short while before that period, the passage through the mouth and neck of the uterus is closed by a viscid mucus, which opposes a firm barrier against the entrance of seminal fluid, and thus prevents the occurrence of subsequent or reiterated con ception. In some of the lower animals, on the other hand, it would appear that several consecutive conceptions not unfrequently occur, and in some animals this may be considered as the natural mode of generation.
It becomes a point of some interest both in a physiological and in a medico-legal view to determine, whether, as has been supposed by some, the same ever takes place in the human species.
The quadrupeds in which superfcetation (as a second conception during pregnancy is called) is said to occur possess a uterus with two horns, and it may be that in them the product of the first conception has occupied only one of the cornua of the uterus, and that the second conception occurred upon the other or empty side. This may be the case in the hare, fur example, which is said to be particu larly liable to superfcetation. In woman also, it has been supposed that a double form of uterus, which is present in rare instances as a malformation of that organ, may admit of a second conception on one side in the course of uterogestation confined to the other. But though this may be regarded as possible, we are not aware that any example of the actual occurrence of pregnancy in both cornua of a double uterus affords a satisfactory proof of it.
Great caution is necessary in admitting the evidence of superfcetation, as many circum stances concur to render it very fallacious. Women occasionally bear twins, or two chil dren differing greatly in size and apparent age; and many are apt at once to form the conclu sion from thence that the two children must have commenced their existence or have been generated at different times ; but it is much more likely in most of these instances, that the different appearance in the size and con formation of the children has arisen solely from a difference in the rapidity and vigour of their growth. In by far the greater num ber of such instances, the smaller of the children bears obvious marks of being stunted in its growth, and it is often deformed, blighted, or dead and shrunk ; and even although this were not the case and the children were both alive, a mere difference of size of children born at the same time must be regarded as very slight evidence indeed of so great a devi ation from the usual phenomena of pregnancy as superftetation.
Those who believe in the possibility of the occurrence of superfcetation found their belief chiefly upon some rare instances of the birth of more than one perfectly developed child at successive periods so remote from one another that both cannot have been conceived at same time, and it must be admitted that these cases, if correct, go far to prove the possibility of superfietation.
In reviewing the cases of alleged super fcetation two questions at once present them selves for consideration, viz. 1st, whether a second conception may take place within a few hours or days after the first, or we may say at any period before the ovum is settled in the uterus; and, second, whether this may occur at a later period, as at two, three, four, or more months after the first conception.