Chemical Changes in Animal Organism. 303 



(B) THE INVESTIGATION OF INTERMEDIARY METABOLISM 

 BY PERFUSION OF THE SURVIVING ORGAN. 



Another method of investigating chemical changes 

 taking place within an organism approximates more closely 

 to the conditions existing in the living animal. This 

 method consists in the perfusion through an isolated organ 

 of the substances the chemical changes of which are to be 

 investigated dissolved in blood, or in a solution of inorganic 

 salts (for mammals usually 0'85 per cent, sodium chloride, 

 with small amounts of calcium chloride, potassium chloride, 

 and sodium hydrogen carbonate, a solution known as 

 Ringer's fluid). Many chemical changes take place during 

 perfusion which do not occur when substances are simply 

 incubated with minced tissue or tissue extracts. This may 

 be due to various circumstances. Some chemical changes 

 are brought about only by the intact cell. Others appear 

 to require the presence of the blood and efficient oxy- 

 genation, the blood acting as oxygen carrier. Others, 

 again, will not occur in the presence of some of the ac- 

 cumulated reaction products, which in the perfusion method 

 are either carried away or destroyed. 



The organ under investigation can be perfused either 

 in situ in the body of the animal, or it can be completely 

 removed from the body and placed in a chamber which is 

 constantly maintained at body temperature, either in air 

 or immersed in a saline solution (0'85 per cent, sodium 

 chloride). The perfusing liquid is led into the organ 

 through the main artery, and finds its exit through the 

 principal vein. The apparatus employed is so constructed 

 that the same fluid is automatically kept in continual 

 circulation through the organ, and at the end of the ex- 

 periment it is examined in order to determine the products 

 of the chemical change of the substance under investiga- 



