NUTRITION AND GENESIS. 483 



constitution which, from this relatively-deficient absorption 

 of nitrogenous matters, is likely to become infertile; as, in- 

 deed, these varieties often do become. Hence, no con- 

 clusions respecting the effects of high nutrition, properly so 

 called, can be drawn from cases of this kind. The cases are, 

 in truth, of a kind which could not exist but for human 

 agency. Under natural conditions no animal would diet 

 itself in the way required to produce such results. And if it 

 did its race would quickly disappear.* 



There is yet another mode in which accumulation of fat 

 diminishes fertility. Even supposing it unaccompanied by 

 a smaller absorption of nitrogenous materials, it is still a 

 cause of lessening the surplus of nitrogenous materials. For 

 the repair of the motor tissues becomes more costly. Fat 

 stored-up is weight to be carried. A creature loaded with 

 inert matter must, other things equal, consume a greater 

 amount of tissue-forming substances for keeping its loco- 

 motive apparatus in order ; and thus expending more for self- 

 maintenance can expend less for race-maintenance. Abnormal 

 plethora is thus antagonistic to reproduction in a double way. 

 It ordinarily implies a smaller absorption of tissue-forming 

 matters, and an increased demand on the diminished supply. 

 Hence fertility decreases in a geometrical progression. 



The counter-conclusion drawn from facts of this class is, 

 then, due to a misconception of their nature a misconception 



* It is worth while inquiring whether unfitness of the food given to them, 

 is not the chief cause of that sterility which, as Mr. Darwin says, " is the 

 great bar to the domestication of animals." He remarks that " when animals 

 and plants are removed from their natural conditions, they are extremely 

 liable to have their reproductive systems seriously affected." Possibly the 

 relative or absolute arrest of genesis, is less due to a direct effect on the 

 reproductive system, than to a changed nutrition of which the reproductive 

 system most clearly shows the results. The matters required for forming an 

 embryo are in a greater proportion nitrogenous than are the matters required 

 for maintaining an adult. Hence, an animal forced to live on insufficientlv- 

 nitrogenized food, may have its surplus for reproduction cut off, but still have 

 a sufficiency to keep its own tissues in repair, and appear to be in good henlth 

 meanwhile increasing in bulk from excess of the non-nitrogenous matters 

 it eats. 



