GENERATION. 



441 



correctly be regarded as the indication of the 

 presence in the system of that quantity of 

 nutrient matter, which, during pregnancy, is 

 destined to serve for the nourishment of the 

 child. We say that this flow does no more 

 than indicate the surplus quantity of blood in 

 the female genital organs ; for, as Burdach 

 remarks, the loss of six ounces of blood for 

 ten successive lunar periods amounts to only 

 three pounds twelve ounces, whereas the foetus 

 and its appendages during that period attain 

 the weight of from ten to fifteen pounds, to 

 which we might add the enormously increased 

 weight of the uterus in order to estimate the 

 whole addition which is made to the uterine 

 system during pregnancy. Again, during lac- 

 tation or nursing the tendency to a super- 

 abundance of blood or plethora in the uterus 

 is generally relieved by the flow of milk from 

 the mammae, which, as has already been 

 remarked, sympathize very constantly with the 

 uterus and other parts of the generative system. 



Such a tendency to plethora as that we have 

 just alluded to, it is scarcely necessary to remark, 

 can have no connexion with lunar or planetary 

 influences, and we are, perhaps, more justified 

 in classing it along with those other changes of 

 the economy which indicate a remarkable ten- 

 dency in the human constitution to periodical 

 recurrence of its actions. 



The crises of fevers on days terminating 

 periods which are most frequently of the dura- 

 tion of seven, fourteen, twenty-one, or twenty- 

 eight days, are of this kind ; and it is deserving 

 of notice that menstruation recurs more fre- 

 quently in periods, the number of days of 

 which are multiplies of seven, than in any 

 others.* 



It has been attempted to be shewn that the 

 male is subject to a periodical plethora in some 

 respects similar to that which gives rise to 

 menstruation in the female, but without any 

 just reason, unless we choose to consider as 

 such the gradual accumulation of seminal fluid, 

 which frequently takes place in healthy men of 

 sanguine temperament, and which gives rise 

 to its periodical emission. 



With regard to menstruation we shall only 

 farther remark that, according to Haller, Bur- 

 dach, and some others, women are more liable 

 to become pregnant immediately or within a 

 few days after the cessation of menstruation 

 than at other parts of the interval ; the probable 

 reason of which will appear from details given 

 in a subsequent part of this article. 



Periodical heat in animals. None of the 

 lower animals in the natural state appear to be 

 subject to anything like a menstrual change or 

 periodical discharge of blood. In lascivious 

 Apes and in some of the domestic animals fed 



* According to the researches of Mr, Roberton of 

 Manchester, detailed in an interesting paper, pub- 

 lished in the Edinburgh Med. and Surg. Journal, 

 vol. xxxviii. p. 237, out of 100 women, in sixty-eight 

 the menstrual discharge returned every fourth week ; 

 in twenty-eight every third week ; in one every se- 

 cond week ; in ten at irregular intervals. These 

 varieties usually exist as family and constitutional 

 peculiarities. 



VOL. II. 



highly, an exudation of bloody mucus from 

 the vagina and external genital organs of the 

 females sometimes occurs, but this is manifestly 

 quite different from menstruation. There is, 

 however, in most of the lower animals a very 

 obvious periodicity in the functions of the 

 reproductive organs; for while the human 

 female is, during a certain period of life, 

 nearly equally fit for propagation at all times, 

 this is the case with very few animals, and, 

 indeed, chiefly among those living in the un- 

 natural state of domesticity. 



At certain seasons of the year there occurs 

 in most of the lower animals a determination 

 of blood to the genital organs of the female, 

 accompanied by sexual desire, which leads 

 them to the propagation of their species. This 

 state of excitement, generally named " the 

 heat,"* lasts for a longer or shorter period; in 

 the ewe for twenty-four hours only, in the 

 cow and mare for a few days, in the bitch 

 nine or ten days, and in the hen-pheasant for 

 as long as two months. In most animals, after 

 it has run its accustomed course, it disappears 

 naturally, but it is more certainly and sooner 

 dispelled by fruitful sexual union. 



The heat belongs more properly to the female 

 than to the male, as there are many species 

 whose females receive the male only at par- 

 ticular seasons, while the male is at all times 

 fit for propagation. In others, constituting the 

 majority of instances, the male organs are sub- 

 ject to the same periodical increase of activity 

 as the female. The male in these animals is 

 usually in heat at an earlier period than the 

 female.f 



In some animals there is a more frequent 

 periodical return of the heat than in others; 

 thus the ewe which remains unimpregnated 

 comes in heat every fourteen days; the cow 

 and some apes, the mare, ass, and buffalo 

 every four weeks; the sow every fifteen or 

 eighteen days ; but in these animals the high 

 feeding attendant on domesticity may very 

 probably occasion a more frequent and less 

 natural return of the period of heat than would 

 occur in the wild state. 



It would appear that the season of the year 

 at which animals most commonly breed is 

 subject to very many and extensive variations, 

 according to the temperature, latitude, and 

 other circumstances connected with the country 

 which they inhabit. 



During the continuance of the heat a peculiar 

 odour is exhaled from the genital organs, and 

 there exudes chiefly from the external organs 

 some bloody mucus, which, in some lascivious 

 apes, resembles blood so much as to have 

 given rise to the belief already alluded to that 

 these animals menstruate. 



Age at which puberty occurs. The appear- 



* Termed the Rut in the deer, wild boar, &c. 



t In some male animals the signs of heat are 

 very apparent. The fine colour of the plumage of 

 most male birds in the breeding season, the deep 

 colour of the comb, &c. in gallinaceous fowls, the 

 thickness and bushy hair of the deer's neck, the 

 greatly enlarged size of the testicles in the cock- 

 sparrow, may be mentioned as familiar examples. 



2 G 



