THEORY OF NUTRITION. 665 



on placing them in an exhausted receiver, those 

 gases exist in a state of merely mechanical mix- 

 ture, and not as organic constituents of the blood. 

 Besides, it has been shown by the microscopic 

 observations of Miiller and others, that the form 

 and magnitude of the red particles are the same 

 in arterial as in venous blood. Nor has there 

 ever been the slightest proof that oxygen causes 

 arterial blood to unite with the solids while passing 

 through the systemic capillaries, nor that car- 

 bonic acid is there received, as it changes to the 

 venous state. We are then bound to conclude 

 that the difference between arterial and venous 

 blood is owing chiefly to the greater amount of 

 caloric and organic matter in the former. It has 

 also been shown in a preceding chapter, (p. 552,) 

 that when the blood of a living artery is confined 

 between two ligatures, or in glass tubes hermeti- 

 cally sealed, it assumes all the properties of 

 venous blood, without the loss of anything except 

 caloric. Moreover, it is manifest, that if the com- 

 position of the solids be renewed, and their tem- 

 perature maintained, at the expense of arterial 

 blood, while the latter is changed to the venous 

 state,* and deprived of its nutritive properties, 



* Physiologists have often asserted, that the paralyzing influence 

 of venous blood when sent to the brain, stomach, and other 

 organs, is owing to some poisonous property which it acquires 

 while circulating through the capillaries. But that its fatal in- 

 fluence is merely negative, owing chiefly to the loss of vital heat 

 in the ultimate tissues, and not to any positively noxious influence, 

 would appear from some experiments of Dr. Kay, (recorded in 



