270 A Manual of Veterinary Physiology. 



actions are rapidly acquired — in fact, would appear to be 

 more highly developed, in the same way that the limbs are 

 more developed in the foal than in the child. In the 

 former, for instance, the limbs from the elbow and stifle to 

 the foot are nearly their full length very shortly after birth, 

 and such joints as the hock are almost the same size as at 

 maturity. 



There are other functions of nerve centres which possess 

 perhaps a greater pathological than physiological interest, 

 viz., the transference and radiation of impressions. An im- 

 pression is transferred, when the animal instead of per- 

 ceiving it as arising from its proper place, believes it to 

 exist in another position. Here the efferent impression, 

 instead of being conducted back from the nerve centre to 

 where the afferent impulse arose, is perceived in another 

 position ; thus thirst is referred to the fauces, colic is 

 referred to the abdominal walls, etc. Some forms of liver 

 disease in the horse have been known to cause lameness in 

 the off fore-leg, evidently referred to the shoulder as in the 

 human subject, in whom also stone in the bladder causes 

 pain in the end of the penis. 



By the radiation of impressions is understood the feeling 

 which refers the impression from a part to exist over a much 

 larger area than that from which it is derived — a familiar 

 example in ourselves is the diffused pain of toothache. In 

 the horse a not uncommon example is the pain found in 

 the leg, generally over the flexor tendons, when pus 

 exists in the foot ; also the diffused pain of colic, though 

 probably the irritating area may be only a few inches in 

 length. 



The majority of physiologists have ceased to describe the 

 radiation and transference of impressions: 1 have intro- 

 duced them here owing to their clinical interest. 



Other functions of nerve centres are Automatism, Aug- 

 mentation, Inhibition, and Co-ordination. By automat ism 

 we understand the power possessed by a nerve centre of 



originating impulses on its own account without any pre- 

 vious stimulation. The nerve changes resulting in the 



