RESPIBATION 



135 



substituted for its blood. The metabolism goes, on actively if the 

 animal is kept in pure oxygen. The taking up of oxygen and giving 

 out of carbonic acid must therefore occur in the tissues, as the animal 

 has no blood. 



The following are the amounts of oxygen used up per minute by 

 one gramme of certain epithelial and muscular organs respectively : 

 Submaxillary gland 0'04 c.c., pancreas 0'05 c.c., kidney 0'03 c.c., 

 heart (contracting very feebly and slowly) 0'007 c.c., muscles of leg 

 (with spinal cord destroyed) 0*003 c.c. 



In order to obtain data, such as the above, it is necessary (1) to 

 analyse the blood going to the organ ; (2) to analyse the blood 

 emerging from the organ ; (3) to determine the 

 amount of blood passing through the organ in 

 one minute. 



Analysis of the blood may be performed 

 by either of two methods, the mercurial air- 

 pump (see Appendix) or the chemical method of 

 expelling the oxygen and carbonic acid from the 

 blood by means of potassium ferricyanide and 

 phosphoric acid respectively. 



Chemical Method of Blood Gas Analysis. 

 When a solution of haemoglobin is treated with 

 potassium ferricyanide it yields all its oxygen to 

 the air on shaking, just as urea yields its nitrogen 

 when treated with sodium hypobromite. The 

 apparatus used for determining the oxygen in 

 blood is very similar to a Dupre's urea apparatus 

 (see p. 142). The blood (5 c.c.) is placed in the 

 large bottle (F) (fig. 40) underneath a layer of 

 dilute ammonia solution. The blood is thus pro- 

 tected from the air, while the apparatus becomes 

 equal in temperature to the bath in which it is 

 placed. The blood is shaken with the ammonia 

 solution which lakes it thoroughly ; the ferri- 

 cyanide solution is then spilt into the laked blood 

 from the tube G, and the oxygen is shaken out of the solution. 

 When the oxygen has been determined the bottle is opened and 

 phosphoric acid is placed in the small tube G : this is subsequently 

 spilt into the mixture of blood, ammonia, and ferricyanide ; it liberates 

 the carbonic acid, which is also shaken out of the fluid. The carbonic 

 acid does not come completely out, however, and a correction has to be 

 introduced for the quantity w 7 hich remains in solution. The gas which 



FIG. 40. Barcroft's appa- 

 ratus for obtaining the 

 blood gases. 



