484: LAWS OF MULTIPLICATION. 



arising partly from the circumstance that the increase of bulk 

 produced by fat is somewhat like the increase of bulk which 

 growth of tissues causes, and partly from the circumstance 

 that abundance of good food normally produces a certain 

 quantity of fat, which, within narrow limits, is a valuable 

 store of force-evolving material. When, however, we limit 

 the phrase high nutrition to its proper meaning — an abun- 

 dance of, and due proportion among, all the substances which 

 the organism needs — we find that, other things equal, fertility 

 always increases as nutrition increases. And we see that these 

 apparently-exceptional cases, are cases which really show us 

 the same thing ; since they are cases of relative innutrition. 



[Note. — By a strange oversight when writing this chapter 

 in the first edition — an oversight I was on the eve of repeat- 

 ing in this present edition — I omitted to bring forward the 

 familiar and all-important evidence furnished by the varia- 

 tions of genesis which ordinarily accompany the alternations 

 of the seasons. These variations, in multitudinous creatures 

 of all types, show unmistakably that reproduction begins at 

 those times of the year when greater warmth and larger 

 supplies of food render maintenance of individual life 

 relatively easy, and when there is therefore a surplus avail- 

 able for producing new individuals. Conversely, along 

 with the decrease of heat and the relative deficiency of food 

 which make it comparatively difficult in winter to maintain 

 individual life, there ceases to be the power of producing 

 other lives: the reproductive organs become quiescent and 

 often dwindle. With this general fact is associated a special 

 fact. Though among wild animals — birds, mammals, and 

 others — breeding ceases when Nature no longer supplies 

 abundant food and warmth; in domesticated mammals and 

 birds, artificially supplied with food and warmth, the breed- 

 ing season is greatly extended and often made continuous, 

 as, under the same conditions, it is in Man himself. 



Evidence yielded by the vegetal world is less conspicuous, 



