450 INTERNAL SECRETIONS 



pelvis and the skull in mammals or the plumage and spurs in 

 birds. Experiments with castration and cross-grafting seem 

 to show that the sex characters are to a certain extent inde- 

 pendent of the sexual hormones. But it must not be forgotten 

 that all these experiments were made on animals in which 

 the sexual differentiation had already been going on for a long 

 time. Sexual differentiation begins during embryonic develop- 

 ment, and at the time of experimental interference the sex 

 characters are already fixed to a certain degree. The different 

 tissues of the organism have a certain growth intensity which 

 can be expressed quantitatively by the number of cell divisions 

 in a unit of time. As was shown by Minot (1908), this rate of 

 growth generally diminishes in proportion to the time which 

 has elapsed after fecundation, and for some tissues, as, for 

 instance, the nerve cells, the rate of growth is nil soon after 

 birth. One might suppose that a tissue, the growth rate of 

 which had already markedly diminished during previous 

 development, would react to the morphogenetic hormones in 

 a less pronounced manner than tissues, the growth rate of 

 which was still at a high level. The experiments of Steinach 

 and my own observations {Lipschutz, igi8 b and 1918 c) supply 

 evidence for such an assumption. 



As we have seen in Chapters VI. and IX., the rudimentary 

 teats and mammary glands of the male guinea pig become 

 transformed under the influence of the ovarian graft into organs 

 similar to those of a female during pregnancy or even lactation. 

 There is not only a feminization, but as Steinach pointed out, 

 an actual hyperfeminization of these organs. On the contrary, 

 the clitoris of the female undergoes beneath the influence of 

 the testicular graft an incomplete masculinization, though 

 other sex characters, such as the psycho-sexual behaviour, 

 may be found markedly changed towards maleness. We have 

 learned that the penis-like organ of the masculinized female is 

 not only shorter than the penis of a normal male, but that 

 there is also a total lack of the corpora cavernosa urethrae. We 

 see that the mammary gland and the clitoris react in a different 

 way, though they are both under the influence of the respective 

 sexual hormones. There is much evidence for the assumption 

 that this difference is caused by variation in growth intensity. 

 The above-mentioned experiments of Steinach were made on 

 animals 2 to 3 weeks old. At this time the mammary gland 



