RESPIRATION. 885 



for heat regulation is abolished and the tissues are unusually heated, 

 as in high fevers. 



Muscular activity augments the gaseous exchanges and so makes 

 the respiratory quotient approach a unit. Other things being equal, 

 man absorbs more oxygen and exhales more carbonic acid than a 

 woman. The exchanges are increased during pregnancy. 



During sleep the consumption of oxygen and the elimination of 

 C0 2 diminish about 6 per cent. This decrease depends upon mus- 

 cular and intellectual repose, darkness, etc. The cells of the tissues 

 determine the amount of oxygen needed, and not an excess of the 

 oxygen present. The intramolecular changes take place in the cells 

 of the tissue, and not in the blood. The amount of water thrown 

 off daily is about a pound; of oxygen taken in, about a pound and 

 one-half; and of carbonic acid thrown off, a little more than a pound 

 and a half. 



In human blood the average total gases are estimated to be, in 

 round numbers, 60 volumes per cent, at C. and 760 millimeters' 

 pressure, made up as follows : 



ARTERIAL, VENOUS 



BLOOD. > BLOOD. 



Oxygen 20 8 to 12 



Nitrogen 1.4 1.4 



Carbonic acid 39 46 



The above table represents the average composition of the gases 

 contained in man's blood. 



A considerable attraction exists between the particles of solid, 

 porous bodies and gases, whereby the latter are condensed within the 

 pores of the solid bodies; that is, the gases are absorbed. Fluids 

 also can absorb gases. One of the functions of the blood is to carry 

 oxygen from the lungs to the tissues and carbon dioxide from the 

 tissues back to the lungs "for expulsion from the economy. These 

 two gases, together with nitrogen, present themselves in two differ- 

 ent states in the blood. The blood, a fluid, must very naturally 

 absorb gases also. Hence one would expect to find 0, C0 2 , and N" 

 held in solution, and also that these gases should behave according 

 to Dalton's law: the amount of gas dissolved in a liquid varies with 

 the pressure of the gas; the higher the pressure, the greater the 

 amount of gas dissolved. But oxygen held in the blood disregards 

 Dalton's law, since its proportions in the blood in various parts of 

 the body remain fairly constant no matter what the pressure, 

 [ence, it owes its presence in and obeys laws dependent upon its 

 ring in the form of loose chemical combinations. If the oxygen 



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