On the Beneficial Action of Certain "Poisons"; and 

 ON the Influence of Poisons on Protoplasm and on 

 Enzymes Respectively. — By D. Fraser Harris, M. D., 

 D. Sc, F. R. S. E., F. R. S. C, Professor of Physiology in 

 Dalhousie University, Halifax, N. S. 



(Read 22 February 1916) 



It would no longer be in accordance with the teachings 

 of physiolog3^ to regard such katabolites asCOo, lactic acid or 

 urea as poisonous or wholly deleterious in the animal body. 

 Just as the heat evolved along with the motion in muscle 

 is not waste or undesirable heat, as much of the heat in the 

 steam-engine is, so the CO2 evolved bj^ tissue-katabolism is 

 not under all circumstances a deleterious or noxious substance 

 to be instantly eliminated. It may serve some good purpose 

 on its way to be excreted. For, first of all, there is no doubt 

 that it is one of the normal chemical stimuli to the activity 

 of the respiratory centre. Normally CO2 constitutes 5-6% 

 of the volume of alveolar air. Any rise above normal in the 

 CO2 concentration in the outer air must retard the elimina- 

 tion of CO2 from the alveoli; this causes CO2 in alveolar air 

 to increase and therefore to increase in the blood, and so 

 produce hyperpnoea, thus: — 



When CO2 is 3% of the inspired air, there is accelera- 

 tion of breathing, when it is 11% of the air, there is distinct 

 hyperpnoea, when it amounts to 15% of the air, there are 

 generalized convulsions, when CO2 rises to 40% of the outer 

 air, it acts as a direct narcotic to the central nervous sys- 

 tem. The converse of all this is that the excessive elimina- 

 tion of CO2 gives an apnoea, a chemical apnoea (Acapnia). 



(2) In the second place, CO2 causes maximal diastolic filling 

 of the heart when it exists in the blood at 5-8%. This is 



(96) 



