388 PHYSIOLOGY. 



obtain the oxygen from the combined haemoglobin. If living tissue 

 is removed from the body and kept warm, moist, and aseptic, it 

 breaks up by hydrolytic cleavage into simpler compounds, just as 

 the tissue does when boiled with acids. This action is called auto- 

 lysis, and is due to intracellular ferments. Pasteur holds that fer- 

 mentation is a general phenomenon in metabolism. Schmiedeberg 

 and others have shown a great number of oxidations taking place 

 in the body which can only ensue through the intervention of intra- 

 cellular ferments, which are called oxidases. 



About one-third of the carbonic acid in the blood is found 

 united with the globin of the red corpuscles, whilst the oxygen is 

 combined with the iron-holding part of the blood. 



Tissue Respiration. The intake of oxygen and the outtake of 

 carbonic acid is only a sort of preparatory phase of the respiration. 

 The real respiration is in the tissues. As has been previously stated, 

 the difference of pressure between the oxygen in the arterial blood and 

 in the tissues easily explains the preponderance of oxygen within the 

 tissues. The elevated temperature also aids the haemoglobin in giving 

 up its oxygen more freely. The tissues have no free oxygen, hence are 

 always hungry for it. The pressure of the carbonic acid is greater in 

 the tissues than in the liquids of the body. 



The oxygen passes from haemoglobin to plasma, then to lymph 

 and from the lymph to the cells of the tissues. The carbon dioxide 

 goes from the tissues to the lymph then to the plasma of the blood. 



The pressure of oxygen in percentages of an atmosphere is as 

 follows : 



External air 20-96 



Alveolar air 16 



Arterial blood 14 



Tissues : 



In the dog, Fredericque gives the tension of carbonic acid in 

 percentages of an atmosphere : 



Tissues 5 to 9 



Lymph 4.4 to 4.9 



Venous blood 3.8 to 5.4 



Alveolar air 2.8 



External air 04 



So often in the study of physiology the student's attention is 

 called to the fact that the movements of the fluids of the body are 

 always in the direction of higher to lower pressure. The explana- 

 tion of the exchange of gases held in loose combination in the blood 



