256 



marrow at the lumbar vertebrae, we do not from this instance of 

 division, although followed, as in the former case, by a suspension 

 or cessation of certain phenomena, infer, as in the former case, a 

 relation of dependence. This objection requires a little explanation. 



17. If the results of the division of a structure prove depen- 

 dence in one instance, they must also be allowed to prove it in 

 another, provided the circumstances of the structure furnish no 

 exception, and provided also the results of the division are the same. 

 These then. are the points to be ascertained in cases where the above 

 distinction is attempted. The question only respects functions, the 

 independence of the assimilating life being necessary. 



18. In these cases, in which dependence is inferred from 

 division of nerves, the function supposed to be dependent ceases 

 immediately upon the prevention of intercourse between the seat of 

 the function and the source of its properties. The function must 

 always cease as soon as the nerve is intercepted, because the proper- 

 ties communicated under a continuity of the nerve cannot assimilate ; 

 if they did, there would be an end of the dependence. Hence, when 

 phenomena immediately succeed to division, we must in every case 

 infer the dependence we are considering ; but if an interval of time 

 elapses between the prevention of intercourse and the cessation of 

 phenomena, than the analogy in this essential circumstance is de- 

 stroyed ; and, for the reason just stated, dependence cannot be in- 

 ferred. Thus, for example, 



19. If the sciatic nerve of a rabbit be divided close to the 

 spinal marrow, the animal, as I have found in the experiment, might 

 become convulsed and die within 36 hours. We do not in this case 

 infer a dependence of the functions of the superior parts of the 

 spinal marrow on properties obtained from the inferior portions of 

 the sciatic nerve, because these functions continue for a time, 

 whereas in the case of dependence they would immediately cease. 

 The functions of the spinal marrow are made to cease by a new 

 relation, which is opened between a disordered condition of the 

 nerve at the place of injury, and the functional properties of the 

 superior parts of the system; just as it is rendered more than pro- 

 bable by the same argument, the action of the heart is maintained 

 by its a'ssimilating life, continuing after the division of its nerves, 

 but is destroyed by a new relation which is opened with it by cer- 

 tain injuries of the spinal marrow. 



20. When functions are made to cease, or life is destroyed by 

 this disordered or foreign state of the properties engaged, it happens 

 either directly or indirectly: directly, as in the example of the sciatic 

 nerve just mentioned, that is, a new relation is opened between 

 vital properties without being produced by disorder of the circula- 

 tion; and indirectly, as when the life of that portion of the brain or 

 spinal marrow which furnishes the power of the respiratory muscles 

 dies, from an injury inflicted upon the superior parts of the brain. 

 Thus a wound of the brain may for thirty-six hours appear to pro- 

 duce but little derangement i at this period phrenitis may supervene. 



