Z%e £Jood. 43 



vacuum the blood froths up and gives off its gases, which 

 are then collected and analysed. 



The gases found are oxygen, carbon dioxide, and nitrogen. 

 The proportion of these found depends upon whether the 

 blood be taken from an artery or a vein ; in the former the 

 oxygen is much larger than in the latter, and the car- 

 bonic acid less. The nitrogen in both cases practically 

 remaining the same. 



At a pressure of 30 inches of the barometer and a tem- 

 perature of 32° F., the following gases are found in 100 

 volumes of blood : 



Oxygen 

 Carbonic acid 

 Nitrogen 



The exact amount of gas varies. The above are mean 

 quantities. 



Oxygen exists in arterial blood in the proportion of about 

 20 per cent. ; whilst in venous blood the proportion is found 

 to vary within wide limits, depending upon the vessel from 

 which it is taken. 



Carotid artery, O 21 percent. Renal vein (kidney active), O 17 per cent. 

 Renal „ „ 19 „ Renal „ (kidney passive), „ 6 „ 



(Landois and Stirling.) 



In the blood of asphyxia oxygen is nearly absent. 



It will be remembered that by far the greater part of the 

 oxygen is in combination with the haemoglobin of the red 

 blood corpuscles. It has been determined that 15 J grains 

 of haemoglobin is capable of absorbing '95 cubic inches of 

 oxygen. The serum of blood contains the oxygen simply 

 absorbed, the amount held in solution is therefore small. 

 The oxygen chemically united with the haemoglobin is quite 

 independent of the laws which regulate the absorption of 

 (see Respiration). 



Besides the vacuum of the air-pump, various chemical 

 substances have the power of deoxidizing the blood-cells, 

 such reducing substances are ammonium sulphide, sul- 



