472 PHYSIOLOGY CHAP. 



adaptation to end of the several voluntary, automatic, and reflex 

 acts must depend. 



Can the cerebellum exert an adjusting effect on the functions 

 of the motor organs without being an organ of conscious sensation ? 

 We need not hesitate to reply to this question in the affirmative, 

 since all the elements of the nervous system, not excluding those 

 of the sympathetic, are usually credited with this adaptive capacity, 

 which may in a wide sense lie termed the regulating or co-ordinating 

 faculty ? By what mechanism is this exerted ? Unless we accept 

 with Flourens an abstract co-ordinating or regulating function in 

 the cerebellum, the only alternative is that the precision and 

 accurate range of movement result from the precision and accurate 

 adaptation of its tonic, sthenic, and static influence. 



The first fact that strikes every one who investigates the 

 intrinsic differences in the three main physiological functions of 

 the cerebellum is that they are so much akin, so intimately 

 connected in their origin, that it is practically impossible to 

 consider them separately and apart. Astasia, in which the 

 deficiency of static action is expressed, is usually held to be a 

 natural effect of asthenia (Tremitus a debilitate); asthenia, by 

 which the loss of sthenic effect in the activity of the muscles is 

 expressed, appears to be related to the atonia observed during their 

 repose. As, however, it is very difficult to demonstrate the relative 

 degree of the three phenomena in decerebellated animals, and as 

 it is not only atonia or asthenia or astasia that is the most 

 pronounced or obvious symptom in such animals, it may be 

 assumed as we said in 1891 that there are only three different 

 extrinsic manifestations of a single process, though there may be 

 no constant relation between their relative intensities. 



In addition to the tonic, sthenic, and static functions, which 

 may collectively be referred to as the "action of reinforcement," 

 the cerebellum normally exercises a direct or indirect trophic 

 action on the organs with which it is in relation. Direct trophic 

 influence is demonstrated by the degeneration and sclerosis that 

 follow ablation of the cerebellum, as shown by the work of Luciani 

 and Marchi, and that of Mingazziiii, Turner and Ferrier, Thomas, 

 Probst, and others. Indirect trophic action is seen specially in the 

 muscular changes observed in cerebellar ataxy, the retarded growth 

 of the cutaneous elements, particularly in the skin, and the lowered 

 resistance of decerebellated animals to the injurious action of 

 external agents, so that they succumb to disease more readily 

 than the intact animal, and have a shorter life in comparison. 



The trophic and functional influences obviously represent the 

 two sides internal and external of one and the same physio- 

 logical process, the intimate nature of which is unknown to us, 

 and of which we perceive only the most striking and obvious 

 effects. 



