Functions of nutrition and assimilation: Digestion, alimentation, growth, temperature of the body, etc.—Respiration and circulation: Pulse, composition of the blood, etc.—Special odour—Functions of communication: Expression of the emotions, acuteness of the senses, etc.—Functions of reproduction: Menstruation, menopause, increase in the number of conceptions according to season, etc.—Influence of environment: Acclimatation—Cosmopolitanism of the genus Homo and the races of mankind—Cross-breeding.
3.—PSYCHOLOGICAL AND PATHOLOGICAL CHARACTERS.
Difficulties of studying them—Immunities—Nervous diseases of uncivilised peoples.
2.—PHYSIOLOGICAL CHARACTERS.
THE differences observable in the fulfilment of the organic functions—nutrition, respiration, circulation of the blood, reproduction, etc.—according to race are unquestionable; but they are still too little studied for us to be able to speak with as much certainty of them as of morphological differences. Further, these functions exhibit so many individual variations that it will always be difficult to rely on averages; besides, the latter present as far as we know a great uniformity.
The functions of nutrition and assimilation scarcely present any varieties according to race. Indigent populations living from hand to mouth by hunting, fishing, the gathering of fruit, etc., exposed to the alternations of famine and plenty, surprise us by their faculty of absorbing a great quantity of food; thus the Eskimo and the Fuegians feed for several days running on a stranded whale. The tendency to obesity is observed in certain races more than in others; very frequent among the Kirghiz, it is rare among their neighbours the Kalmuks, etc. The early obesity of Jewish women, which is besides artificially fostered in Africa and in the East, is also to be noted. Growth in different races would prove of some interest, but investigations into this subject have been made only in Europe and America.[116] Great difficulties stand in the way of these inquiries among uncivilised peoples, as it is almost impossible to ascertain the exact age of individuals. In a general way stature and weight increase with age somewhat irregularly, and as if by fits and starts; almost always a period of rapid growth in height succeeds a period of calm, during which the dimensions of the body increase in width (shoulders, pelvis, etc.). It has also been remarked that growth in height is especially rapid from the month of April to July and August, that it diminishes from November to March; and that, lastly, weight increases especially from August-September to the end of November. Sexual differences make themselves felt from birth. We have already seen (p. [26]) that at birth the stature of boys exceeds that of girls by a figure which varies from two to eight millimetres (.08 to .32 of an inch), let us say of half a centimetre (less than the quarter of an inch) on an average. During the first year stature increases very rapidly: the child a year old is one and a half times as tall as at birth. The increase is less rapid until the fourth year, when the height is double what it was at birth. From the fourth year the growth is a little slower till the age of puberty, when there is a fresh start, and when the sexual differences are especially marked; girls grow more rapidly than boys between ten and fifteen years of age, but after fifteen boys take the lead and grow at first quickly, then slowly till their twenty-third year, at which age they have almost attained the limit of their stature; while women seem to stop growing at twenty.
The size of most of the organs increases pretty regularly; the heart in girls at the age of puberty and the brain in the two sexes are the only exceptions to this rule. The weight of the brain is 2 1⁄2 times greater at one year than at birth, 3 1⁄3 at five years, 3.7 at ten, and 3.9 at fifteen; later its growth diminishes, to reach its maximum before the age of twenty, 4 times its initial weight, and to decline slightly after forty or forty-five years.
At birth the brain represents 12.4 per cent. of the total weight of the body, at a year old 10.9 per cent., at five 8.4, at fifteen 3.8, and at twenty-five 2.3 per cent. only.[117] Unfortunately we have hardly any parallel observations on non-European populations. The only observations of this kind based on a sufficient number of subjects (several thousands) relate to the Japanese. According to Baelz, the stature of the Japanese increases after the age of puberty only 8 per cent., whilst it increases 13 per cent. among Europeans. On the other hand, Drs. Hamada and Sasaki say that growth diminishes greatly among Japanese men from sixteen or eighteen, and is found to be completely arrested at the age of twenty-two.[118] There is abundance of evidence that Negroes, Melanesians, and Malays attain their maximum height between eighteen and twenty-one. Dietary regimen and comfortable circumstances have a great influence on growth, as I have already said when speaking of stature (p. [31]).
The activity of transformations in the system certainly presents differences according to climate, but not according to race. Thus the alimentary supply is conditioned solely by the heat required.[119] The temperature of the body hardly varies two or three tenths of a degree, for instance, among two peoples so different as regards type and mode of life as the French of the north and the Fuegians. In fact, the temperature taken in the mouth is from 37.1° to 37.2° C. among the former and 37.4° among the latter.[120] Besides, among Europeans the individual variations range between 37.1° and 37.5° C. Among Negroes the temperature appears to be, on the contrary, a little lower than that of Europeans.
Let us pass on to the respiratory functions. The vital capacity or the quantity of air in the expanded lungs, which is 3.7 cubic metres among the English according to Hutchinson, and from 3 to 4 cubic metres among Europeans in general, falls to 3 metres among the Whites and the Indians of the United States (Gould), and even to 2.7 among the Negroes of this latter country. The difference is very trifling; however, it has to be taken into consideration, seeing that among Europeans persons of high stature have an absolute capacity superior to that of people of low stature. Frequency of respiration seems to be greater among uncivilised peoples than with Europeans (14 to 18 respirations per minute); it is from 16 to 20 respirations among the Fuegians, 18 to 20 among the Mongol-Torgootes, 19 among the Kirghiz, and 18 among the Afghans.[121]