LETTERS TO BROTHER JOHN. 277 



I believe it is possible, by very rapid exertion, 

 to fill almost every vein in the body with arterial 

 blood. I have not room, here, to detail the obser- 

 vations which have led me to this conclusion ; but 

 I do not speak unadvisedly. Nor would the secre- 

 tion of bile be stopped by this state of things ; for 

 it has been proved, that although, under ordinary 

 circumstances, it is secreted from venous blood, 

 yet it can be secreted from arterial. 



Now, I do not mean to say that it would be 

 advisable for you to arterialize the whole of your 

 blood. And there is no fear of it ; for it would re- 

 quire greater exertion than any man would, or even 

 could, voluntarily undergo. But be assured of this, 

 that the greater the quantity of arterial blood, and 

 the less the quantity of black venous blood, con- 

 tained in your body, the stronger, aye, and the 

 happier and more light-hearted, you will be ; and 

 the only means of arterializing the venous blood is 

 bodily exertion. The elasticity of mind, and joyous- 

 ness of heart, which EXERCISE proverbially affords, 

 are the direct result of an increase in the quantity 

 of arterial, and a decrease in the quantity of venous, 

 blood. The increase of animal spirits, as well as 

 the increase of animal strength, must always cor- 

 respond with the increase of arterial blood. 



