DUCTLESS GLANDS AND INTERNAL SECRETIONS 293 



The sympathy between ovaries and mammary glands is further 

 shown by the remarkable fact that a cow ovariotomised when 

 in full milk remains in milk for two or three years. The influence 

 of the ovaries on psychic conditions is well recognised : some 

 forms of vice in the mare are cured or improved by removal of 

 the ovaries. It is to be noted that apparently the complete 

 removal of all trace of ovarian tissue in the cat and dog may not 

 invariably prevent periodic sexual excitement (Leeney). It has 

 been stated that the removal of the ovaries from the dog affects 

 metabolism, especially the consumption of oxygen, which falls 

 off, and that this may be neutralised by the administration of an 

 extract of ovary ; this causes the metabolism to rise above the 

 normal, but does not affect the unoperated animal. 



Similarly, there can be no doubt as to the testicles forming 

 an internal secretion. It is fair to assume that among other 

 functions the implantation of the characteristics of the male, 

 especially the aggressive characteristics, must be regarded as 

 part of its duty. Otherwise it is difficult to account for the 

 alteration in character which occurs as the result of complete 

 castration, and the modifying change which follows from leaving 

 some of the epididymis attached to the cord. Castration does 

 not appear to lead to any important loss of muscular energy 

 or power of withstanding fatigue. The influence of the testicles 

 on the growth of bone is recognised in man ; the long bones 

 continue to grow, due to the delay in the ossification of the 

 epiphyses ; the same is said to have been observed in animals, 

 but of this, so far as we know, there is no evidence. The effect 

 of castration on the eating properties of flesh is well known. Its 

 influence on the thymus gland is also very marked ; instead of 

 disappearing at puberty, castration causes the gland to become 

 larger and more persistent. The effect of removal of the testicles 

 and ovaries on the dog, cat, deer, and birds, may be conveniently 

 considered in the chapter on Generation and Development. 



The adaptation of the digestive fluids to the nature of the 

 food has been referred to (p. 192). This and the influence of a 

 fixed diet in producing a more effective digestive secretion, and 

 the harm resulting from sudden changes in diet (p. 257), may 

 possibly be regulated by a specific chemical excitant. These 

 are matters of the highest practical importance in the feeding 

 and management of animals. 



The chief lesson that the present work on internal secretions 

 teaches is that an organ apparently functionless may be per- 

 forming some office of the highest importance, while even those 

 actively employed in the preparation of an obvious secretion 

 may, in addition, be carrying out important chemical activities 

 — the liver, for example, with its external secretion of bile and 



