38 



one to think that the recovery wonhl have lieen more eomplete if tlie ease liad 

 been treated soon after tlie accident. 



Tliere is anotlier way of looking at the problem, and perhaps it comes nearer 

 if not (]nite to the solution. We said in the above that there was at first some 

 obstruction, whatever that may have been, at the point of the injury in tiie cord, 

 and as a result it caused the muscles below the |)oint of injury to degenerate 

 from disuse. The obstruction in the cord perhaps after awhile was removed, and 

 it may have been at the time of the operation by the surgeon. 



Let us now look to the laboratory and see if we can find evidence to aid us in 

 solving the problem. It is a well known fact that there are nerve fibers tliat liave 

 a controlling effect on the calibre of blood vessels, or to state it more exactly, 

 they hold the unstriped muscles in a certain state of contraction. It is known to 

 physiologists as tone. This may be demonstrated by cutting the l)ranches of the 

 sympathetic system that supply tlie blood vessels of the ear of a rabbit. As a 

 result the ear becomes flushed with blood, showing that the tone of the vessels is 

 lost. It makes it more certain if the end of the severed nerve that supplies the 

 ear is stimulated artificially, when it once more returns to the normal. If tiie 

 stimulant be strong enough, it will so contract the coats of the vessel that the ear 

 will appear pale. When we turn to the skeletal muscles, it does not appear quite 

 so clear that they are influenced by the tonic effect of nerves. The observations of 

 different investigators are at variance on this point. I believe that the pre- 

 ponderance of evidence goes to show that there is a tonic effect, or at least nerves 

 which control the nutritive functions, or have what is known to physiologists as a 

 trophic action. Taking, for instance, the severance of the sciatic nerve of an 

 animal, and we will find that the muscles become flabby and that they do not 

 possess the resistance that is noticed when the nerve is intact. 



Time will not permit me to go into the argument showing that trophic centers 

 exist in the cord. But assuming that these centers do exist, let us see how they 

 carry out their work. In the first place, reasoning from the analogies of the 

 action of the heart and other centers, we might with some reason suppose that the 

 trophic centers, by virtue of their own metabolism, send out de novo efferent 

 impressions to the muscles, thus having a nutritive effect. If we carry the 

 analogy farther, we will have as good a reason for assuining that there are afferent 

 impressions that pass to these ceiiti'rs and, as it were, inodify the efferent 

 -impressions. There is experimental evidence to show tiiat this is true. Ff)r 

 instance, if the posterior root of a nerve is severed, while the anterior root i.s. 

 intact, it results in a loss of tone to certain muscles. 



