104 



THE VERTEBRATE ANIMAL: METABOLISM 



from the organs of external respiration, enters into combination 

 with the haemoglobin of the red blood cells. These materials, 

 which are necessary for maintenance of the chemical reactions of 

 the protoplasm, are carried into capillary networks all over the 

 body, and pass from the blood into the lymph and so into the cells 

 where they are used. Carbohydrates and fats may be left in large 

 amounts at storage depots, to be picked up later for distribution. 



Fig. eO.^Schematic figure of blood capillaries and lymphatic vessels in 

 relation to cells throughout the body. A maximum of intercellular space is 



shown. 



a, artery; b.c, blood capillaries; c, cells; i.c.l.s., intercellular lymph spaces; 

 phatic vessel; I.e., lymph capillaries; v, vein. 



/, lym- 



Carbon dioxide, water, and nitrogenous wastes, produced by oxida- 

 tions within the cell, pass out into the lymph and so into the blood 

 plasma in the capillaries. Water and carbon dioxide are carried 

 directly to places of excretion; nitrogenous wastes are trans- 

 ported to the liver where the urea is formed, to be taken to the 

 kidneys. The exchange of foods and excretions between blood 

 and cells by way of the lymph can apparently be adequately 



