44 STELLA BURNHAM VINCENT 



endings in the muscles and joints which results from the unusual 

 body position. 



It is easy to see, if we take Sherrington's view of the cere- 

 bellum as the head ganglion of the proprio-ceptive system with 

 the labyrinthine centers as the most important ones, how by 

 means of the large cerebellar tracts in the cord connections with 

 the periphery are established. The cerebellar connections of the 

 fifth nerve can be seen : but Sherrington and others consider the 

 peripheral elements centering here to be those coming from 

 muscles and joints, which being phylogenetically very old and 

 dealing with constant habitual states, function in an unconscious 

 way in maintaining skeletal tonus and bodily attitude. To these 

 other kinaesthetic components must be added the cutaneous. 

 Sherrington would say, probably, that the cutaneous element 

 was only the precursor and not a real part of the proprio-ceptive 

 reflex. Others would say that these cutaneous elements are on 

 the same level as the kinaesthetic and for the most part are only 

 physiologically sensory, not consciously so, and need involve no 

 cortical connection. 



Sherrington says of these reflexes, "It is difficult to see how 

 a steady mechanical stimulus can continue to elicit a reflex 



constantly for long periods If a weak agent is to 



stimulate, its application must be abrupt. But in the tonic 

 reflexes whose source lies at the proprio-ceptors a weak stim- 

 ulus, although apparently unchanging, seems to be an effective 

 stimulus." Thus these reflexes differ very much from other 

 reflexes in the threshold value of the stimulus, fatigueability, 

 and in the time factor: but when the afferent element fails or 

 changes quickly, as in the illustration of the running rat, there 

 come instant, quick, preserving reflexes, which usually involve 

 the other systems also. In the case given of anaesthesia of the 

 feet, any cortical control was impossible and the peripheral end 

 of the lower arc was cut off. It was not merely that sensation 

 was lacking or changed but that the end organ was incapable 

 of functioning. 



Whatever may prove to be the cause of the many slips and 

 falls, white rats, even in their natural conditions, have a very 

 unstable equilibrium. The most common pathological condi- 

 tion which one sees among them is a twisting of the head and 

 upper part of the body to one side so that the animal in running 



