ii SENSIBILITY OF THE INTEENAL OEGANS 79 



developed into tadpoles. . . ." Two interesting conclusions can 

 be drawn from these experiments : 



(a) The sexual impulse in toads and frogs is more potent than 

 the most painful sensations these animals can undergo. 



(6) Eemoval of the most sensitive parts and of the whole brain, 

 including of course the olfactory and visual organs, does not 

 inhibit the sexual clasp nor interrupt it if already in progress. 



Goltz continued Spallanzani's experiments on spawning frogs, 

 and tried in particular to solve three problems : 



Which part of the body of the female exerts the attractive 

 force on the male that leads to copulation ? By what sensory 

 paths is the male attracted towards the female and led to copulate ? 

 On what part of the nervous system does the persistent muscular 

 contraction by which the male embraces the female depend, and 

 by what paths is this centre excited ? 



On these points Goltz came to the following conclusions : 

 (a) At the breeding season every part of the body of the female 

 attracts the male. This was proved by a number of curious ex- 

 periments in which the female was successively deprived of 

 different organs (the ovaries, sense organs, the whole of the skin, 

 etc.) without checking the impulse of the male to copulation. In 

 fact the male will even embrace the dead female. 



(6) The male is attracted to the female from afar not by one 

 sense, fcut by all the senses that can come into play. Goltz showed 

 that all the sense organs successively can be removed from dif- 

 ferent males, without their ceasing to copulate with the female. 



(c) The centre on which the clasp depends lies in the upper 

 segment of the cord. The activity of this centre is excited by 

 the mechanical cutaneous stimuli of pressure or friction. Goltz 

 proved that the clasp persisted, not only after decapitation, 

 as seen by Spallanzani, but even after transverse section of 

 the cord between the third and fourth vertebra, or after both 

 these operations. If after isolating the thoracic portion, including 

 the three upper vertebrae and the whole thoracic girdle, from the 

 rest of the body in a frog, the skin of the breast and flexor surface 

 of the arms is stroked, the arms will clasp the finger of the 

 operator in a firm clasp which grows stronger if the friction is 

 repeated. If the breast is skinned, or the three dorsal roots 

 which it contains are cut, this reflex spasm no longer takes place. 



Tarchanoff continued Goltz' experiments on the frog and 

 succeeded in isolating the stimulus that produces sexual desire 

 in the male ; it is due to the tension in the seminal vesicles when 

 the spermatic fluid collects there. While no other mutilation 

 disturbs the copulating male, which persists, as we have seen, after 

 removal of heart, lungs, and testicles, the moment the seminal 

 vesicles are taken away, or merely opened and emptied, the clasp 

 ceases at once, or does not occur if not already begun. On the 



