CHAP, v.] THE SPINAL CORD. 597 



calf may be thrown into action by tapping the tendo Achillis ; and 

 in some cases the same muscles may be made to execute a series of 

 rhythmic contractions, by suddenly pressing back the sole of the 

 foot so as to put them on the stretch. These, and other instances 

 of a like kind, at first sight appear to be, and indeed it has been 

 maintained that they are, cases of reflex action, due to afferent 

 impulses started in the tendon; hence they have been frequently 

 spoken of as 'tendon-reflex.' But the evidence, on the whole, 

 shews that they are not reflex, but due to direct stimulation 

 of the muscles. Nevertheless, and this is the interesting point, 

 they are closely dependent on the integrity of the spinal cord, and 

 of the connections between the cord and the muscles. In the case 

 of animals they disappear when the spinal cord is destroyed, or the 

 nerves going to the muscles are severed or even when the posterior 

 roots only are divided. And in the case of man they are diminished 

 or wanting in certain diseases of the spinal cord (locomotor ataxy), 

 and exaggerated in others ; so much so indeed that they have be- 

 come of practical clinical importance as a means of diagnosis. With- 

 out discussing the matter any further, we may say that such pheno- 

 mena indicate that the nutrition and the irritability of a muscle 

 are in some way governed by influences of one kind or another 

 which proceed from the spinal cord, and which, in certain cases at 

 all events, are the result of, or are determined by, influences of a 

 similarly obscure nature reaching the cord from the muscles by the 

 posterior roots of the spinal nerves. 



