518 PHYSIOLOGY CHAP. 



excitant of those glands, and the English authors' theory of 

 "chemical co-ordination," .generally speaking, are ill-founded. 

 Certain experiments in our own laboratory deserve mention, in 

 relation to the point we are now discussing, because the method of 

 experiment lends itself to the solution of this problem. U. 

 Lombroso in collaboration with Bolaffio employed the method of 

 parabiosis (supra, p. 102) between virgin and pregnant rabbits. 

 The animals experimented on only survived at most for nine days ; 

 but no trace of modification was ever detected in the mammary 

 gland of virgin rabbits, although the iodine test proved that active 

 exchanges took place between the two animals. It should be 

 remembered in judging the negative value of these results in 

 regard to the hormone problem, that in the virgin rabbit the 

 mamma is reduced to six or seven simple tubules, and that it ex- 

 hibits profound modifications even by the third day of pregnancy. 



In rats, which longer survive the effects of parabiosis, no 

 appreciable modifications could be seen in the virgin mamma, 

 although the time was greatly extended. 



An observation of Morpurgo's on a parabiotic couple of mixed 

 sex supports these negative results. The female became pregnant 

 after four months' parabiosis, was delivered at term, and suckled 

 her young, but there was no sign of lactation in the male. 



All these observations (while still insufficient) militate not 

 merely against the theory that the foetus discharges a specific 

 substance into the maternal blood by which the development of 

 the mammary gland is stimulated, but, generally speaking, against 

 the theory that development is activated by any chemical stimulus 

 circulating in the blood. 



XI. The much-debated question of whether the human skin 

 is capable of absorption must not be omitted from this chapter. 

 While apparently lending itself to easy solution by experiment, 

 it is on the contrary a difficult problem, judging from the amount 

 of literature on the subject, and the contradictory results arrived 

 at by different workers. 



With the exception, as we have seen, of the palms of the hands 

 and soles of the feet, which have no sebaceous glands, the whole 

 surface of the body is lubricated with the sebum secreted by 

 these glands, owing to which the horny layer of the epidermis 

 is rendered highly impermeable to water even with prolonged 

 immersion. After a hot bath of 30-60 minutes, the epidermis 

 of the palm and sole alone is visibly softened, showing that the 

 skin is unsuited for absorption of water or substances dissolved 

 in it. 



The method of weighing the subject before and after total 

 immersion in a bath is obviously inadequate evidence for this 

 statement. In fact, the experiments by this method of Jamin and 

 De Laures (1872) gave conflicting results ; sometimes there was 



