86o THE SPINAL CORD. 



this criterion, all purely spinal reactions fail to evince features of con- 

 sciousness. If two frogs, the one spinal, the other intact, be placed 

 together in water which is then gradually warmed, the intact animal, 

 as the water approaches 35 C., exhibits movements significant of effort 

 to escape. But the spinal frog will not move, though the temperature 

 rise to even fatal height, so long as the ascent be gradual. A spinal frog 

 placed direct from cold water into water at 35 C. exhibits at once 

 lively movements, but these, in view of their above-mentioned absence 

 under the other condition, are no sign of associative memory. They 

 may therefore be unconsciously reflex. Not so the reactions of the 

 intact frog. 1 



Such a view of the relation of spinal reflexes to consciousness 

 corrects a tendency to see in such reflexes the germs of volitional acts. 

 The mainsprings in the evolution of volition are feeling and perception. 

 From reactions unconscious, and therefore devoid both of feeling and 

 of perception, volitions cannot have sprung. On the other hand, our 

 individual experience shows how readily volitional acts by repetition 

 and practice ultimately become actions involving neither attention nor 

 even consciousness, create, in fact, habitual reflexes. The spinal re- 

 flexes may be regarded as descended from volitional acts, inherited and 

 therefore instinctive habits of simplest order, testifying to a so-to- 

 say primitive process akin to memory in the spinal cord. 2 It might be 

 thought that, arisen thus, they would be most in evidence in the spinal 

 organ of the most elaborated nervous systems. As a fact, they are there 

 less obtainable and seem there less active than in simpler systems. This 

 may be due to the greater solidarity of the whole nervous system in its 

 higher than in its lower forms. The greater solidarity renders the more 

 severe the injury wrought by mere isolation of any part from the 

 whole. And this the more so that in higher animals the great project- 

 ing senses of the cranial region dominate the spinal cord and actuate 

 the motor organ, the skeletal musculature of the whole body, more 

 than in lower forms. 



SPINO-CEREBRAL AND CEREBRO-SPINAL KEACTIONS. 



The spinal cell systems are not concerned only with reactions con- 

 fined in their extension to the cord. They also transmit, on the one 

 hand, impulses to nerve cells in the brain, and, on the other, receive 

 impulses from nerve cells in the brain. The cell systems in the brain 

 seem able to discharge all efferent root cells, especially those of the 

 skeletal musculature. This is implied in the old remark that " to move 

 things is all mankind can do." On account of its connections with 

 the brain, the spinal cord has therefore to be studied in respect of (1) 

 the elaboration of cutaneous, muscular, and visceral sensations ; and 

 (2) contractions of the skeletal, vascular, and visceral musculature in 

 response to stimulation of the cranial sense organs; and (3) as the 

 instrument of emotional and intended movements. Many of the reflex 

 arcs commencing in the spinal afferent root cells lead vid encephalon 

 back to the spinal cord again, involving cerebral links. These reflex 

 arcs, in their course, react on and are reacted on by arcs based upon 



1 F. Goltz, "Beitr. z. Lehre v. d. Nerv. d. Frosches," Berlin, 1868. 



2 Hering, "Ueber d. Gedachtniss als allg. Funct. d. organisirt. Materie," Sitzungsb. d. 

 k. Akad. d. Wissensch., Wien, 1870. 



