446 PHYSIOLOGY CHAP. 



elude that the asthenic and astatic phenomena are intimately 

 connected with the atonic symptoms ; this agrees well with our 

 conception of the physiology of the cerebellum. 



A general fact to which there has been no exception in our 

 numerous experiments on dogs and monkeys is that the phenomena 

 of deficiency consequent on complete unilateral extirpation of the 

 cerebellum are limited exclusively to the neuro-muscular system ; 

 sensation is not disturbed. 



We more particularly investigated the tactile and muscular 

 sense. 



On merely touching a normal dog while it is eating, or while 

 its eyes are bandaged, or, better, while it is suspended in the air by 

 means of a sling with the limbs hanging down (Hitzig's method), 

 it shows by a swift movement of reaction that it has noticed the 

 contact. If the tactile sensibility of the decerebellated dog is 

 tested in the early post-operative period, when the animal is still 

 incapable of standing or walking, the reactions to contact are 

 usually absent in the limbs both of the operated and of the normal 

 side, and there may be no reactions to slight painful sensations of 

 any kind, particularly upon the operated side. 



But if the examination is repeated three to four weeks after the 

 operation, at the time when the locomotor ataxy is at its maximum, 

 the reactions to contact never fail; only they occur with a 

 perceptible delay on the operated, as compared with the normal, side. 

 Finally, during the period which may last over a year in which 

 the cerebellar ataxy is final and permanent, with no prospect of 

 improvement, the animal reacts to slight contacts with equal 

 promptness on either side. This shows that unilateral removal in 

 the cerebellum does not disturb tactile sensibility. 



It is more difficult in animals to make any exact investigation 

 of the so-called " muscular sense " by means of which we are aware 

 of the position of our limbs, the direction of active and passive move- 

 ments in the same, and the degree of tension or resistance opposed 

 to muscular contraction, without the aid of tactile sensibility and 

 vision. Of these different forms or qualities of muscular sense, the 

 first, which conveys the sense of the position of the limbs, is easy 

 to examine in dogs. When a normal dog with its eyes bandaged 

 is kept upright on a table, and any one of the four limbs is brought 

 into an unnatural position, e.g. when the dorsal surface of the foot 

 is placed in contact with the table, the limb is brought back 

 instantly to the normal position ; if one of the four legs is left 

 unsupported, by letting it hang over the edge of the table, the 

 animal at once draws it up and puts it back on the table. 



In the dog after removal of half the cerebellum it is impossible 

 to carry out this experiment successfully while the animal is still 

 unable to stand on its legs, and therefore to react to unaccustomed 

 postures, even when perfectly aware of them. When it begins to 



