160 



niSCOVRRY 



different supply and demand influences, show a com- 

 mon tendency to rise or to fall, then it is fairly safe 

 to assume that the change has been in the currency 

 in which the prices are expressed, and not in each 

 commodity. 



The general idea is well illustrated by the fact that it 

 was once believed that, because the stars all appeared 

 to move across the sky, the earth was at the centre of 

 the universe and the heavenly bodies moved round it. 

 It is now thought more reasonable to suppose that it is 

 we who arc moving by reason of the revolution of the 

 <-arth and that the stars are relatively fixed. 

 (To be continued.) 

 BOOKS 

 Stabilising lite Dollar, by Irving Fisher. (Macmillan, i8s.) 

 The Purchasing Power of Money, by Irving Fisher. {Ibid. 12s. 6d.) 



The Place and Power of 

 the Cerebellum 



Bv D. Fraser Harris, M.D., D.Sc, 

 F.R.S.E. 



Pro/essor 0/ Physiology, Dalhousie Uniuersily, HnU/nx, X.S. 



The functions of the cerebellum were for a very long 

 time a mystery ; our anatomical knowledge of it was 

 so much more detailed than the physiological, a state of 

 matters that has been the usual rather than the excep- 

 tional as regards most organs of the body. 



The cerebellum, which is below the cerebrum, and 

 protected from its pressure by a stout sheet of con- 

 nective tissue, the tentorium, is composed of two 

 lateral portions, the hemispheres, and a single central 

 mass, the vermis. Each half of the cerebellum is con- 

 nected by many nerve-fibres to the cerebrum above, to 

 the spinal cord behind, and to the brain-stem below, the 

 superior, inferior, and middle peduncles respectively. 



The cerebellum sends nerve-fibres to the cerebrum 

 by a crossed path, and the cerebrum sends fibres by a 

 •different and more roundabout crossed path to the 

 cerebellum. These reciprocal relations are of such a 

 kind that when one-half of the cerebrum, say the left, 

 does not develop, the opposite, or right, half of the 

 cerebellum remains undersized. 



The cerebellum is also abundantly related to the 

 body through certain tracts of the spinal cord, the chief 

 connection being with the skin and muscles of the body 

 by tracts which do not cross ; that is, the left side of 

 the body is represented in the left half of the cerebellum 

 and the right in the right. The right half of the cere- 

 bellum is, therefore, connected with the left half of the 

 brain, but with the right half of the body. Now, it 

 will be remembered that the left half of the brain 

 governs the right half of the body. The muscles of 



the head, neck, and trunk are represented on both 

 sides of the mid-line in the central parts of the cere- 

 bellum, those of the limbs in the lateral parts. 



The cerebellum is late of appearing in the nervous 

 system as we ascend the animal scale. As one might 

 expect, it is relatively very large in the birds, creatures 

 to whom the maintenance of an accurate balance is so 

 very important. The fishes, for instance, have the 

 cerebellum better developed than have the reptiles, in 

 which group it cannot have much functional importance. 



Let us now try to make out what these various con- 

 nections of the cerebellum to other parts of the nervous 

 system mean. In the first place, injuries to or diseases 

 of the cerebellum do not produce any impairment of a 

 person's sensations. Animals from which the entire 

 cerebellum has been removed do not suffer any loss of 

 sensation. A man with congenitally undevelojjed 

 cerebellum has no diminution of delicacy of sensation. 

 The cerebellum is, therefore, not the physical basis of 

 the elaboration of sensations, nor does it aid in that 

 process. 



But numerous nerve-impulses travel over the paths 

 which reach the cerebellum through the spinal cord 

 from the body — impulses, therefore, which are afferent 

 but not sensation-producing or sensificatory. The 

 cerebellum receives but it does not perceive. Muscles, 

 joints, skin, viscera, and those curiously complicated 

 " semicircular " canals, a part of the internal ear 

 which have to do with balancing, all send their impulses 

 to the cerebellum. But they also send impulses which 

 go to the cerebrum and giv-e rise to sensations of 

 different degrees of distinctness. So that the state of 

 matters seems to be this : while certain organs send 

 impulses to the brain to contribute to consciousness, 

 these same organs simultaneously send impulses to the 

 cerebellum, which do not give rise to consciousness. 



We cannot, therefore, speak of the cerebellum as 

 being " aware " of anything ; there is no simple word 

 to express what exactly the cerebellum does as regards 

 afferent impulses. It receives them from many parts 

 of the body and " works them up " or correlates them 

 without their arousing consciousness at all. The 

 cerebellum receives afferent but not sensificatory im- 

 pulses, and dealing with them subconsciously, relates 

 them to outgoing impulses. 



Let us in the next place see what is the state of 

 matters on the efferent or motorial side. When a 

 portion of the cerebellum is injured in an animal, the 

 animal does not suffer from paralysis of any muscles, 

 but from a clumsiness of movement and an awkward- 

 ness of muscular action. When this awkwardness is 

 brought out in the arms as a test in clinical medicine 

 it is called " adiadochokinesia." The muscles have, 

 indeed, rather less tone than before (atonia), and their 

 movements are somewhat inco-ordinate, or ataxic. 



