SUMMARY '.VI') 



tion of a fibrous material called fibrin, resulting from the 

 action of an enzyme and a calcium salt on a soluble protein 

 called fibrinogen. The fibrin entangles the corpuscles and 

 forms the blood clot. 



Oxygen, as has been noted, serves as a source of energy 

 to the various tissues, the waste product being carbon 

 dioxide. The lungs of the animal, which are a mass of tissue 

 containing minute air cells, are the seat of the transfer of 

 oxygen and carbon dioxide in the blood. When air is drawn 

 into the lungs, oxygen passes through the capillaries of the 

 blood, which surround the air cells, dissolves in the blood 

 plasma and then unites with the haemoglobin. At the same 

 time, carbon dioxide dissolved in the plasma passes through 

 the capillaries into the lungs, and sodium bicarbonate in the 

 plasma breaks up into sodium carbonate and carbon dioxide, 

 which dissolves in the plasma and passes out through the 

 capillaries as before. After the blood thus charged with 

 oxygen and relieved of carbon dioxide is forced into the 

 tissues, oxygen passes from the plasma through the capil- 

 laries into the lymph surrounding the tissues. Oxyhemo- 

 globin breaks up as a result of this decrease in the amount 

 of dissolved oxygen. Dextrose is oxidized in the tissues; 

 carbon dioxide is eliminated in the lymph from which it 

 passes through the capillaries to the blood plasma and 

 combines with sodium carbonate to form the bicarbonate. 



The tissues of the bodv are all bathed in a fluid called 

 lymph which is derived from the blood by diffusion of the 

 plasma through the capillaries. The tissue spaces filled with 

 lymph unite to form lymph vessels, which permeate the 

 body in every direction, combining sooner or later to form 

 the main lymph channel called the thoracic duct. Lymph 

 vessels pass through a series of enlarged bodies called lymph 

 glands which serve among other things as the principal 

 source of the white corpuscles. The composition of the 

 lymph is very similar to blood plasma, containing the same 

 compounds, although not exactly in the same proportions. 



The animal compounds are somewhat similar to plant 

 compounds, the principal difference being the carbohydrate, 

 glycogen, which corresponds in formula to starch and 



