THE FUTURE 185 



and pour into the system various fluids known as " hor- 

 mones." Comparatively little is yet understood of the 

 work of these glands, but enough has been ascertained 

 to prove that their functions are very important. The 

 injection into the blood of extracts obtained from them 

 has produced most remarkable results. Goitre is reduced, 

 as a rule, by the injection of extract of the thyroid gland. 

 A singular result is the development of a cock's comb 

 on the head of a hen as the result of injecting testicular 

 extract. These glands, in fact, seem to control the growth 

 and functions of the various organs. Now, as the nutritive 

 condition of the germ cells is probably governed by the 

 central nervous system through the medium of the blood, 

 and as these glands which pour their secretions into the 

 system must also be controlled by the nervous system, it 

 seems fairly clear that we have in these three, the nervous 

 system, the glands, and the circulatory system, the great 

 regulating mechanism of the organism. Probably the 

 whole metabolism and development of the organism from 

 childhood to old age is controlled by the acceleration or 

 retardation of the work of these glands. And it is not 

 improbable, therefore, that the secretions of some of 

 them play a powerful part in the nourishment of the 

 germ cells, and thus regulate fertility. 



Another factor to be studied is that presented by the 

 constituents of food known as " vitamines." Experi- 

 ments have shown that if fowls are fed on polished rice 

 or other foods deficient in vitamines, they fall victims 

 after a period to beri-beri and other diseases ; while if 

 vitamine starvation be carried far enough death ensues. 

 We need some intelligently directed experiments to 

 ascertain the effects of both a deficiency and a super- 

 abundant supply of vitamines on fertility. Not a great 

 deal has been done in this direction yet. McCarrison has 



