FACTS 187 



described, some of the gates were furnished with automatic 

 alarms against certain robbers and gave no sound against 

 others. Only, there is this to reassure the owner of the 

 palace in presence of robbers for whom the gates ring no 

 alarm, they also do not open or, at least, do not open enough 

 for the safety of the palace to be threatened. 



In other words, every agent penetrating into the organism 

 through a sensitive epithelial surface determines in the 

 protoplasm of that surface a rupture of equilibrium which 

 is the starting point of a reflex. 



Nerve Centres 



The bodies of the neurons n (Fig. 15) are seldom isolated 

 in the animal. Oftenest they are found associated in greater 

 or less number in masses called ganglions, or nerve-centres. 

 At these centres there arrive in great number the cylindraxes 

 from various epithelial cells ; these are called centripetal 

 nerve filets because they bring the influx to a centre. From 

 these centres there also issue a great number of cylindraxes, 

 called centrifugal nerve filets, because they carry the influx 

 starting from a centre either to a muscle or gland or to some 

 other nerve centre. 



We can easily understand that, when different parts 

 of the body are in possession of their own special nerve 

 centres, they are more or less independent of each other. 

 In the general co-ordination they are related to each other 

 only by the network of nerves which bring the centres into 

 communication with each other. 



In this book we have to occupy ourselves only with that 

 which is general among all living beings. There is no need 

 of lingering over the nervous system, since plants have 

 but a rudiment of it (protoplasmic continuity). But in 

 biology that which interests man the most is man himself, 



