220 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



by many observers.* It is, in fact, not essentially different per- 

 haps from the second phase of the first group of theories. Those 

 who have expressed their idea of the physiology of the cerebellum 

 by saying that it is a center of the muscle sense have, in recent 

 times at least, recognized that this sense has a cortical center also in 

 the cerebrum. The view can not assume, therefore, a conscious 

 muscle sense mediated by the cerebellum, but only that the muscle 

 sense fibers have a cortical termination therein and that the cerebel- 

 lar activity thus aroused is in some way necessary to the orderly 

 adjustment of complex voluntary movements. According to an- 

 other point of view, the cerebellum is a great augmenting organ for 

 the neuromuscular system. It is added on, as it were, to the cere- 

 brospinal motor system and serves not to co-ordinate the motor 

 discharges, but to increase their strength or effectiveness. This 

 general view, first proposed by Weir Mitchell (1869), has been sup- 

 ported by Luys, and especially, although with important modifica- 

 tions, by Luciani. f Some of the details of the work of the latter 

 observer are given below. 



Experimental Work Upon the Cerebellum. Rolando, and par- 

 ticularly Flourens, gave the direction to modern experimentation 

 in this subject. The latter observer made numerous observations, 

 especially on pigeons, in regard to the effect of removing all or a 

 part of the cerebellum. He describes in detail the striking results 

 of such an operation. When all or a large part of the organ is re- 

 moved the animal shows a most distressing inability to stand or 

 move. There seems to be no muscular paralysis at all, but, at first, 

 a total lack of power to co-ordinate properly the contractions of the 

 various muscles involved in maintaining equilibrium. The animal 

 takes a most abnormal position, with the head retracted and 

 twisted, and any attempt to move is followed by violent disorderly 

 contractions that may result in a series of involuntary somersaults. 

 The animal is totally unable to fly. When the injury to the cere- 

 bellum is less the effect upon the movements is either too slight 

 to be noticed or is shown in a greater or less uncertainty in its 

 movements. When it attempts to walk, for instance, it exhibits 

 a staggering, drunken gait, a condition designated as cerebellar 

 ataxia. Similar operations on mammals give in general the same 

 results. If the operation is unilateral, that is, affects only one 

 hemisphere, the animal (dog) exhibits forced movements, such 

 as a tendency to roll around the long axis of his body toward the 

 injured side and subsequently movements in a circle toward the same 



* See Lewandowsky, " Archiv f. Physiologie," 1903, 129. 



t For the literature of the cerebellum see Luciani, "II cervelleto," Florence, 

 1891; German translation, "Das Kleinhirn," 1893. Also Luciani, article, 

 "Das Kleinhirn " in "Ergebnisse der Physiologie," vol. iii, part n, p. 259, 1904. 



