512 LAWS OF MULTIPLICATION. 



nutrition, we may suspect that it is in part due to greater 

 muscular expenditure. A kindred fact, admitting of a 

 kindred interpretation, may be added. Though the com 

 paratively-low rate of increase in France is attributed to 

 other causes, yet, very possibly, one of its causes is the 

 greater proportion of hard work entailed on French w r omen, 

 by the excessive abstraction of men for non-productive 

 occupations, military and civil. The higher rate of multipli 

 cation in England than in continental countries generally, is 

 not improbably furthered by the easier lives which English 

 women lead. 



That absolute or relative infertility is commonly produced 

 in women by mental labour carried to excess, is more clearly 

 shown. Though the regimen of upper-class girls is not what 

 it should be, yet, considering that their feeding is better than 

 that of girls belonging to the poorer classes, while, in most 

 other respects, their physical treatment is not worse, the 



duals constituting any race of organisms, presupposes conditions so favoui- 

 able to life that the race can be in no danger ; and that rapidity of multi 

 plication becomes needless. Conversely, he argues that a deplethoric state 

 implies unfavourable conditions implies, consequently, unusual mortality ; 

 that is implies a necessity for increased fertility to prevent the race from 

 dying out. It may be readily shown, however, that such an arrangement 

 would be the reverse of self-adjusting. Suppose a species, too numerous 

 for its food, to be in the resulting deplethoric state. It will, according to 

 Mr. Doubleday, become unusually fertile ; and the next generation will be 

 more numerous rather than less numerous. For, by the hypothesis, the un 

 usual fertility due to the deplethoric state, is the cause of undue increase of 

 population. But if the next generation is more numerous while the supply 

 of food has not increased in proportion, then this next generation will be in 

 a still more deplethoric state, and will be still more fertile. Thus there will 

 go on an ever-increasing rate of multiplication, and an ever-decreasing share 

 of food, for each person, until the species disappears. Suppose, on the 

 other hand, the members of a species to be in an unusually plethoric state. 

 Their rate of multiplication, ordinarily sufficient to maintain their numbers, 

 will become insufficient to maintain their numbers. In the next generation, 

 therefore, there will be fewer to eat the already abundant food, which be 

 coming relatively still more abundant, will render the fewer members of the 

 species still mor^ plethorig, and still less fertile, than their parents. And the 

 actions and reactions continuing, the species will presently die out from abso 

 lute barrenness. 



