498 VETERINARY PHYSIOLOGY 



(iii.) Van Slyke has devised an apparatus for the hberation 

 of the CO2 of the blood by weak sulphuric acid and of the 

 Oo by potassium ferricyanide. The gases are then collected 

 in a Torricellian vacuum and measured at atmospheric 

 pressure. The method may be carried out in a few minutes 

 and is of use in clinical work. 



Amounts of Gases. — The amount of gases which may be 

 extracted varies considerably. About 60 c.c. of gas, 

 measured at 0° C. and 760 mm. pressure, from 100 c.c. 

 of blood may be taken as a rough average. The proportion 

 of the orases varies in arterial and venous blood. 



Average Amount of Gases per Hundred Volumes 



OF Blood. 



Recently a series of analyses of the arterial and venous 

 blood in normal men has been made, and it has been found 

 that the average content is about 



In the lungs the blood gains about 5 per cent, of oxygen 

 and loses about 5 per cent, of carbon dioxide. 



While there is an exchange of something hke 36 per 

 cent, of the oxygen, the exchange of carbon dioxide amounts 

 to only between 8 and 9 per cent, of the total amount in the 

 blood. 



In the tissues there is, of course, a reversal of the changes 

 that go on in the lungs. 



VI. Source of the Blood Constituents. 



A. Plasma. — The water of the blood is derived from the 

 water ingested. But there is a free interchange of water 

 between the blood and the tissues so that after bleeding 

 water rapidly passes into the blood to make up the original 



