OTHER FUNCTIONS OF THE SPINAL CORD. 155 



Hearing from injury ; but there can be little doubt that those which we are 

 constantly witnessing in other animals, possessing large external ears, are 

 reflex actions excited by the irritation applied to them. In regard to the Nose, 

 we find a remarkably complex action that of Sneezing adapted to drive off' 

 any cause of irritation ( 189). It will Hereafter be shown that the stimulus 

 is conveyed, in this case, not through the Olfactory nerve, but through the 

 Fifth pair ; so that it is not dependent upon the excitement of the sensation of 

 smell. The act of Coughing, also, may be regarded of a protective character, 

 being destined to remove sources of irritation from the air-passages. 



XII. Other Functions of the Spinal Cord. 



207. The influence of the Nervous Centres in maintaining what is com- 

 monly designated as the tone of the muscular system, was first distinctly 

 limited by Dr. M. Hall to the Spinal Cord, and the system of nerves connected 

 with it. By the expression in question is meant, that state of moderate con- 

 traction which causes all the muscles to present a certain degree of firmness, 

 by their antagonism with each other, when none of them are particularly con- 

 tracted or relaxed. The following experiments by Dr. M. Hall clearly prove 

 the influence of the Spinal Cord on this functional condition : " Two Rabbits 

 were taken ; from one the head was removed ; from the other also the head 

 was removed, and the spinal marrow was cautiously destroyed with a sharp 

 instrument : the limbs of the former retained a certain degree of firmness and 

 elasticity ; those of the second were perfectly lax." " The limbs and tail of a 

 decapitated Turtle possessed a certain degree of firmness or tone, recoiled on 

 being drawn from their position, and moved with energy on the application 

 of a stimulus. On withdrawing the spinal marrow gently out of its canal, all 

 these phenomena ceased. The limbs were no longer obedient to stimuli, and 

 became perfectly flaccid, having lost all their resilience. The sphincter lost 

 its circular form and contracted state, becoming lax, flaccid, and shapeless. 

 The tail was flaccid and unmoved on the application of stimuli." It is proba- 

 ble that this tonic contraction is strictly a reflex action ; an impression of 

 the condition of the muscle, corresponding with the " muscular sense" of Sir 

 C. Bell, but not necessarily accompanied by sensation, being conveyed to the 

 Spinal Cord, and producing the stimulus to contraction. The want of this 

 tone is seen in the relaxation of the sphincters ; and also in the distortion of 

 the face, produced by paralysis of the Portio Dura, and resulting from the 

 tonic contraction of the muscles on one side of the face, unbalanced by that 

 of the other side. Cases have occasionally presented themselves, in which 

 the portio dura has been paralyzed to the influence of the Will (owing to 

 disease affecting its Cerebral termination), whilst its Spinal connections have 

 not been affected ; so that the tone of the muscles has been preserved, and no 

 distortion of the face has 'manifested itself, until the muscles were stimulated 

 by a voluntary impulse, to which those of one side only would respond. 



208. Nearly allied to this function of the Spinal Cord, is that by which it is 

 subservient to the maintenance of the contractility of muscles paralyzed to the 

 influence of the will. It is well known that, in ordinary cases of paralysis, 

 the muscles lose their irritability in the course of a few weeks, so that no 

 stimulus excites them to contraction; and it is also \Vfell known that their 

 characteristic structure is so greatly affected, that, in progress of time, no true 

 muscular fibres can be detected in their place. Experiments on animals, in 

 which portions have been removed from the nerves supplying the limbs, con- 

 duct to exactly the same result as the experiments made for us by diseased 

 conditions in Man. Now Dr. M. Hall has pointed out that, in cases where 

 the muscles are paralyzed to the influence of the will, through disease of the 



