202 CIKCTJLATION 



blood the carbohydrate, together with certain poisons 

 (see p. 142). The carbohydrate thus separated is 

 either stored in the Uver as glycogen, or given out 

 as needed in the form of gi'ape sugar to the hepatic 

 vein. This hepatic vein passes this grape sugar and 

 the other unchanged nutrients into the general cir- 

 culation by opening into the inferior vena cava. 



The poisons are passed into the liver secretion or 

 bile and returned to the intestine with that fluid for 

 removal with the faeces. 

 (&) Fats are collected by the lacteals, and enter the 

 veins by way of the thoracic duct at a point just under 

 the left collar bone where the left jugular and left 

 arm vein join. Thence they pass into the heart by 

 the superior vena cava. 



2. Oxygen enters the blood in the lungs, and is con- 

 veyed to the heart by means of the pulmonary veins. We 

 shall consider this phase of the circulation more in detail 

 in our study of respiration. 



The loading of blood with waste. — All veins carry 

 wastes (CO2, urea, etc.), which they collect from the tis- 

 sues. This waste either enters the blood directly by way 

 of the capillaries, or else enters the lymphatics and thus 

 the veins by the thoracic duct or right lymphatic duct. 

 The right lymphatic duct enters at the joining of the 

 right jugular vein and the right arm vein. 



Unloading of nourishment by the blood. — All arteries ' 

 carry food and oxygen to the tissues which they supply, 

 and deliver these substances to the cells of the tissues 



' The pulmonary veins and arteries are exceptional in that the piil- 

 monary veins carry oxygen laden blood, and the pulmonary arteries, 

 carbon dioxide laden blood. 



