MAN CONSIDERED PHYSIOLOGICALLY. 667 
up to about the fortieth year of life or later, puberty is that 
period of life which is most remarkable for sudden, striking de- 
velopment. While this is in some respects most pronounced in 
the sexual organs and related parts, as the pelvis and mammary 
glands of the female, yet a whole host of other changes take 
place simultaneously, in such a way as to leave no doubt that 
they are related to those of the sexual organs. Not only the 
characteristic form of the body, but the psychic peculiarities of 
the sexes, appear and become fully established with an extraor- 
dinary rapidity. 
There is, therefore, no period of life fraught with so much 
of developmental good or ill as puberty. A host of diseases 
may now show themselves, according to the laws of heredity, 
as a result of deficient resistance, etc. 
The Sexes.— While the differentiation of sex becomes greatly 
more pronounced at puberty, there are decided differences be- 
tween the male and female infant. The male from birth is the 
taller and the heavier. This inequality is maintained in adult 
life. The average woman is shorter and lighter than the man; 
her muscular and bony systems are less developed, both abso- 
lutely and relatively; her brain is some ounces lighter; her 
blood is poorer in hemoglobin, of lighter specific gravity, and, 
as a whole, less in quantity. Woman’s metabolism, if we may 
judge by the income and expenditure, is both absolutely and 
relatively less. Man’s physical strength is nearly double that 
of woman. 
These facts have an important bearing on some of the burn- 
ing questions of the day. There are, it will be seen, deep-lying 
differences between the sexes, which can not be ignored in our 
education and civilization generally, without running counter 
to that sexual differentiation which Nature, through long ages, 
has been bringing toward higher and higher development. 
Old Age.—From middle life onward, in most persons, there 
is a gradual process of deterioration going on in every tissue. 
Elasticity diminishes and rigidity of tissues becomes more and 
more marked. The arteries undergo changes which, whether 
fatty or calcareous, greatly impair their usefulness; the carti- 
lages of the ribs and other parts tend to become calcareous, so 
that the chest-walls possess less of elasticity; this, combined 
with a general impairment of muscular power, lessens the 
capability of thoracic movement. Protoplasm everywhere has 
less vital potential, so to speak; hence with the approach of old 
age we often find adipose tissue in excess. It becomes a bur- 
