184 



VETERINARY PHYSIOLOGY 



(a) This training or preparation of the brain is in part 

 hereditary. Each member of a species is born with well- 

 estabhshed lines of action in the process of development, and 

 throughout life these inherited channels play an important 

 part in determining the results of stimulation. In young 

 fowls, as soon as they are hatched, the acts of running and 

 of pecking are at once performed, and in many families 

 particular gestures or expressions follow certain modes of 

 stimulation in many different individuals without the 



Fig. 93. — Diagram of collateral connections of different parts of the cere- 

 bral cortex, a, b, c, pyramidal cells of the cortex, all connected by 

 collateral branches with other parts of the cortex in the same and in 

 the opposite hemisphere, a give ofiF the pyramidal fibres to the cord. 

 {After Ramon y Cajal.) 



consciousness of the person being involved. They are 

 inherited cei^ebral reflexes, (h) Paths may also have been 

 developed in the individual as the result of previous activities 

 of the nervous mechanism. For, if a given action has once 

 followed a given stimulus, it always tends to follow it again. 

 This, in fact, is the basis of all training of animals — to open 

 up paths in the nervous system by which the most suitable 

 response may be made to any given stimulus, and to prevent 

 the formation of paths by which inappropriate reaction may 

 be produced. 



(2) The nutrition of the hrain. — Not only will the 

 previous training of the brain thus act as the directive force 

 in the response to stimuli, but the nutrition of the hrain 

 also plays an important part. The action of a brain when 

 well nourished and freely supplied with pure blood is often 

 very different from that of the same brain when badly 

 nourished or imperfectly supplied with blood. 



