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



cerned, therefore, we must look to the spinal centres alone for explan- 

 ation of the phenomenon. The rise of blood pressure which occurs 

 in the first stage of asphyxia might be held accountable for the exalt- 

 ation of the knee jerk ; but that this is not the true explanation seems 

 evident, owing to exaltation being met with in anaemia of the cord, 

 and in the marked fall of blood pressure in general blood letting. 

 That it is due to an irritable condition of the lumbar cells induced 

 by depriving them of their normal supply of oxygen is rendered 

 probable from the following facts, as well as those just mentioned. 



What part, if any, the presence of excess of carbonic acid in the 

 lumbar centres plays in the production of the phenomenon, it is diffi- 

 cult to estimate. That the absence of oxygen is alone capable of 

 producing it is shown by the effects of anaemia of the cord, and by 

 the fact that when nitrogen gas is inhaled the same result is obtained ; 

 for in this latter instance most of the oxygen in the body is used up, 

 and the nitrogen takes its place, but there is not necessarily any 

 excess of carbonic acid, since there is no obstruction of expired air, 

 merely the entrance of nitrogen instead of oxygen being provided 

 for. One thing is, however, evident, viz., that in all these conditions 

 the effect is not so rapid as in asphyxia ; therefore it is not improbable 

 that the presence of excess of carbonic acid hastens the results. 



The abolition of the knee jerk might be due to exhaustion of the 

 lumbar centres by the asphyxia! convulsions, for Beevor* has shown 

 that after severe epileptic convulsions in man the knee jerk may be 

 abolished, and this has been attributed to exhaustion of the lumbar 

 centres, consequent on their great discharge of energy. That this is 

 not the explanation of the phenomenon in asphyxia is proved by the 

 fact that it occurs when the spinal cord has been divided transversely 

 in the dorsal region prior to the occurrence of asphyxial convulsions, 

 and where, therefore, the lumbar cells are not discharged daring the 

 asphyxial spasms, and consequently cannot be exhausted in this way. 

 Indeed it appears not improbable that the effects in man which have 

 been attributed to exhaustion of the lumbar centres may after all be 

 due to the asphyxiated condition of the blood, which occurs in a severe 

 epileptic seizure, consequent on the arrest of respiration due to the 

 tonic spasm of the muscles of respiration. 



That the failure of the knee jerk is consequent on the fall of blood 

 pressure which takes place in the third stage of asphyxia seems 

 improbable, as the knee jerk is lost just when the blood pressure 

 commences to fall, often, indeed, before there is any distinct evidence 

 of the decline of blood pressure. Then also in general loss of blood 

 the blood pressure falls very considerably lower than the height at 

 which it stands when the knee jerk is lost in asphyxia without any 

 sign of loss of knee jerk, which does not take place till much later. 



* Loc. ext. 



