SEXUAL BEHAVIOUR 87 



usually due to this, and when the adrenal overgrowth is 

 cut away, the ovaries are able to exert their influence once 

 more so that a reversion to the female type follows. 



3. HORMONES AND SEXUAL BEHAVIOUR 



Consideration must now be given to the effects of the 

 gonad hormones on behaviour since almost all those who 

 have correlated the condition of the gonads with sexual 

 activity have done so on the assumption that this 

 activity is due to the actions of these substances on the 

 nervous system. As long ago as 1903, when the study of 

 hormones was still very much in its infancy, Bouin and 

 Ancel*o concluded that it is the gonad interstitial tissue 

 which, 'par sa secretion interne^ tient sous sa dependance 

 Vardeur genitale\ Also, as long ago as 19 10, Steinach^^^ 

 suggested that courtship and copulatory behaviour were 

 dependent on the 'erotization' of the nervous system by 

 the gonad hormones, but attempts to prove this had to 

 wait until these substances had been analysed and 

 manufactured in a pure state. 



Actually the first attempts to induce behaviour 

 changes by chemical means were made not with the 

 gonad hormones but with extracts of the anterior 

 pituitary. It was found that these extracts, when injected 

 into newly-hatched male chickens, caused them to crow 

 when only 9 days old and to attempt to copulate when 

 only 13 days old.^i Later it was found that normal 

 courtship activities could be induced in the same way in 

 the lizard Anolis carolinensis in winter, ^^ as well as in 

 the arioestrus horse, 102 cat,!^* and dog. 125 \i is now 

 evident that such stimulation is obtained at second hand 

 through the induced activity of the animal's own testes 

 or ovaries. 



Attempts to by-pass the gonads and to induce a direct 

 effect on behaviour were next made with the gonad 

 hormones themselves and from the beginning the effects 

 of the injection of male hormone were dramatic. In most 



