574 THE SPINAL CORD. 



than that which results in animals from experimental interference, clinical 

 experience tends, on the whole, to support the view that in man the more 

 complete subordination of the spinal cord to the brain has led to the dying 

 out of the complex reflex actions which are so conspicuous in the lower 

 animals. This, however, cannot be regarded as distinctly proved. 



When we come to study voluntary movements, we shall see reason to 

 think that in man, as in the lower animals, the will in carrying out these 

 movements makes use of complex nervous mechanisms situated in the 

 spinal cord nervous mechanisms into the working of which, as urged 

 above, afferent impulses enter largely ; and it seems improbable that these 

 spinal mechanisms should be capable of being thrown into action by the 

 will only. In the act of walking, for instance, it is highly probable that 

 the movements of the legs are the direct results of the action of nervous 

 mechanisms in the lumbar cord brought into play by the will, being thus, 

 in an indirect manner only, the products of volitional impulses ; and even 

 in man, though clinical experience only affords us instances of this machin- 

 ery working apart from the brain in a damaged condition and under unfa- 

 vorable circumstances, so that the resemblance of the movements observed 

 to the complete act of walking is but feeble, still it seems similarly probable 

 that under more favorable circumstances the lumbar cord separated from 

 the brain might as part of a reflex act carry out the movements in a more 

 complete and coordinate manner. 



505. We have dwelt above chiefly on reflex actions, in which the 

 efferent impulses cause contractions of skeletal muscles, since these are 

 undoubtedly the most common and the most prominent forms of reflex 

 action ; but it must not be forgotten that the efferent impulses of reflex 

 origin may produce contractions of other muscles, as well as other effects, 

 such as secretion, for instance. On several of these we have dwelt, from 

 time to time in previous parts of this work, and it will be unnecessary to 

 repeat them here. But it may be worth while to point out that the spinal 

 cord, by serving as a reflex centre for innumerable ties which correlate the 

 nutritive or metabolic activities of the several tissues to events taking place 

 in other parts of the body, plays a conspicuous part in securing the welfare 

 of the whole body. In dealing ( 462) with the general problems of nutri- 

 tion, we stated that an orderly nutrition appears to be in some way depend- 

 ent on nervous influences. Many of these nervous influences appear to 

 issue from the spinal cord, either as parts of a reflex act or as the outcome 

 of some automatic processes. When in a dog the lumbar cord is wholly 

 separated from the rest of the cord by section, the nutrition of the hind 

 limbs and the general health of the animal may, with care, be maintained 

 in a very satisfactory condition ; but if that small separated piece of the 

 cord be destroyed, death inevitably ensues before long, in spite of every care 

 and precaution, being brought about apparently by the disordered nutrition 

 of the hind limbs and other parts supplied by nerves coming from the lum- 

 bar cord. In man extensive injuries to the spinal cord are followed by bed- 

 sores and other results of impaired nutrition ; and, indeed, death is gen- 

 erally brought about in this way in cases of paraplegia caused by accidental 

 crushing or severance of the cord. 



506. Inhibition of reflex action. The reflex actions of the spinal cord, 

 like other nervous actions, may be totally or partially inhibited, that is to 

 say, may be arrested or hindered in their development by impulses reaching 

 the centre while it is already in action. Thus, if the body of a decapitated 

 snake be allowed to hang down, slow rhythmic pendulous movements, which 

 appear to be reflex in nature, soon make their appearance ; all these may 

 be for a while arrested by slight stimulation, as by gently stroking the tail. 



