LESSON V 



THE SOURCES OF LOSS AND OF GAIN TO THE 

 BLOOD 



1. General Review of the Gain and Loss.— The 



blood which has been aerated, or arteiialised, by the 

 process described in the preceding Lesson, is carried from 

 the lungs by the pulmonary veins to the left auricle, and 

 is then forced by the auricle into the ventricle, and by the 

 ventricle into the aortsi. As that great vessel traverses 

 the thorax, it gives off several large arteries, by means of 

 which blood is distributed to the head, the arms, and the 

 walls of the body. Passing through the diaphragm (Fig. 

 47, Ao.), the aortic trunk enters the cavity of the abdomen, 

 and becomes what is called the abdominal aorta, from 

 which vessels are given off to the viscera of the abdomen. 

 Finally, the main stream of blood flows into the iliac 

 arteries, whence the viscera of the pelvis and the legs are 

 supplied. 



Having in the various parts of the body traversed the 

 ultimate ramifications of the arttjries, the blood, as we have 

 seen, enters the capillaries. Here the products of the 

 waste of the tissues constantly pour into it ; and, as the 

 blood is everywhere full of corpuscles, which, like all 

 other living things, decay and die, the products of their 

 decomposition also tend to accumulate in it, but these are 

 insignificant compared to those coming from the great 

 mass of the tissues. It follows that, if the blood is to be 

 kept pure, the waste matters thus incessantly poured into, 



