454 Mr. J. S. R. Russell. Circumstances under which [May 18, 



these poisons have acted on them for a certain time, just as when 

 they have been deprived of a certain amount of their supply of 

 oxygen. That they should fail to act after they have been subjected 

 to the influence of such powerful poisons is not surprising. It may, 

 of course, be urged that the results obtained with these drugs are 

 not the result of their specific action on the lumbar centres, but of 

 the want of oxygen. While it cannot be denied that this may play 

 some part in the prod action of the phenomena, that the direct action 

 of the poisons is mainly responsible there can be little doubt, for 

 during the respiration of these vapours, in the manner employed in 

 their administration to animals, the entrance of atmospheric air is 

 not excluded, so that, while possibly the interference with the supply 

 of oxygen to the lumbar centres might account for the preliminary 

 exaltation of the knee jerk, it can never be nearly so great as to 

 bring about the abolition of the knee jerk, which, as has been shown, 

 takes a considerable time to disappear, even after the fresh supply of 

 oxygen to the blood has been completely cut off. Farther, and this 

 is more convincing, the effects of chloroform and ether respectively 

 differ in two important respects, since (1) the effects on the knee jerk 

 are brought about very much more rapidly when chloroform is inhaled 

 than when ether is administered, and (2) the effect produced by 

 chloroform continues longer after its administration is discontinued 

 than does the same effect when produced by ether. JSothing but 

 certain inherent properties of these drugs can be reasonably believed 

 to be the causes of these differences, for, if venosity of blood was 

 alone or mainly responsible for the results, the effects produced by 

 ether should be more rapid and powerful than those produced by 

 chloroform, since greater venosity is observable in the case of the 

 former than the latter drug. It seems not unreasonable to assert, 

 therefore, that the results obtained with ether and chloroform are 

 mainly due to the direct action of these drugs on the lumbar centres. 



IV. The Effect of Ancemia of the Spinal Centres. 



Deprivation of the lumbar cord of its blood supply, either by direct 

 pressure on the abdominal aorta or by general blood letting, is 

 synonymous with depriving it of its normal supply of oxygen. But 

 another factor has to be taken into consideration in this relation, for 

 both of these methods of experimentation are attended with notable 

 lowering of the blood pressure in the lumbar cord. That the shock 

 occasioned by such lowering of blood pressure, whether resulting 

 from the more or less sudden effect of clamping the aorta, or the 

 more gradual lowering in general loss of blood, is capable of causing 

 abolition of the knee jerk is not improbable ; but that this is the true 

 explanation of the occurrence of the phenomena is made improbable, 



