THE STRUGGLE FOR LIFE. 215 
purveys nutriment to the tissues, andi also: partly takes. up 
the waste of the body. The capillaries end in the: smaller 
veins, which themselves keep on uniting: into: larger and. 
larger trunks, and finally pour their contents into: the. right 
side of the heart, whence it is sent into. the lungs. Here 
a similar distribution and: re-collection takes place, and; 
during this process, the- blood’ being: exposed! in. the walls 
of the air-cells to the air, absorbs Oxygen, its impurities 
are. burnt off and expelled from the. body through the air 
passages, chiefly in. the. form of Carbonic Acid: After. this 
process, the purified blood!is again returned to the left side 
of the heart, thence again to be sent in a vivifying stream. 
through all the tissues of the body. If; however; the-air- 
cells of the lungs are blocked up so that’ there is insufficient 
exposure to the Oxygen of the: air, the blood leaves them 
unpurified and the whole. body gradually dies, poisoned’ by 
its own waste. To make my scheme: complete, I must 
add, that in one part: of the body, viz: the liver, the 
venous blood: coming from the alimentary canal/is distri- 
buted and re-collected' in a method similar to that. seen. in 
the lungs, before it mingles with the. rest of’ the. venous 
blood. destined’ to. be poured: into. the right side off the 
heart. This, however, is effected’ without the: aid of) any. 
subsidiary. pump. 
By means of the circulation, the blood is brought. within 
the reach of every: cell’ of the: body, andi not: only. brings 
nourishment to it; but also-carries.away from it the. products. 
of its own waste, substances. which, if not removed; would 
quickly poison not’only. the cell ‘itself; but also.its neighbours. 
In addition to. this method of removing. waste, another 
system: of vessels exists, called: Lymphatics, which. also. 
help. in the removal ‘of used-up- material, and’ convey. it, by. 
means which I need) not: specify, to discharge: it’ into the 
great vein at the root of the neck. The-contents: of these. 
lymphatics is calléd Lymph, and during, its- journey, it: 
