HEREDITY 207 



One of the reactions that nourishment produces 

 on the palate is to awaken the activity of the 

 salivary glands. These sensitive nerves advise the 

 nervous centres, by means of thin centripetal 

 currents, of the organic irritability produced in 

 them by the presence of nourishment, and these 

 centres immediately send to the glands, by thin 

 centrifugal fillets, an amount of energy propor- 

 tionate to the sensation received ; a reflex action, 

 the modus operandi of which is understood on 

 noting in fig. 23 how the centrifugal nerve-termina- 

 tions reach the cells, in order to be transformed 

 immediately on their arrival into chemical work, 

 the result of which is the secretion of the saliva. 



The contact of the aliment with the palate is not 

 indispensable in order to excite the glandular 

 activity. The idea is the motive force ; a proof of 

 which, though it may be deemed trivial, is that the 

 sight of a toothsome article of food is sufficient to 

 produce an effect whereby the mental representation, 

 that is, the idea, which in this case is the initial 

 energy, may provoke in the sensitive nerves of the 

 salivary glands the action necessary to increase the 

 secretion of saliva; and hence the proverb above 

 mentioned. 



We have quoted this example because in the 

 male and female genital glands the spermatoblasts 

 and ovoblasts are cells, and, like all the other glands, 



