Human Physiology. 211 



becomes a foul mass of disease and putrefaction. Both are 

 vital processes, and their being vigorously and perfectly carried 

 on is a matter of vital importance. 



The action of the lungs in both the vivification and purifica- 

 tion of :he blood has been already noticed. Every air-cell of 

 the lungs is both a secreting and excreting organ. It secretes 

 oxygen from the air for the blood; it excretes carbonic acid, 

 and much other waste matter from the blood, which goes out 

 to mingle with the atmosphere. The air should never be 

 breathed twice, for two reasons. It is deprived of a part of its 

 oxygen, and is thus rendered less fit for respiration; but it is 

 also loaded with carbonic acid and other matter which should 

 never be taken a second time into the system. It may be still 

 worse to breathe over the breaths of other people. Our rooms 

 should be so ventilated that every breath we draw should be as 

 pure as the outer atmosphere. But our houses, our bedrooms, 

 and still more our churches and theatres, schools and public 

 rooms of all kinds, are often very imperfectly ventilated, and 

 sometimes simply pestilential. The lungs themselves become 

 diseased when required to act upon a foul atmosphere, and the 

 blood may acquire more impurities through them than it is 

 able to get rid of. The lungs, that so readily absorb ether or 

 chloroform, probably take in, in the same way, the matter 

 which causes typhus and cholera. 



The liver, if we judge from its size, must be a purifying 

 organ of great importance. It is the largest gland in the body, 

 weighing three to four pounds, and is about twelve inches long, 

 by six or seven wide. It is composed of an immense number 

 of separate glands, each supplied with its nerves, its proper 

 arteries and veins for its own nutriment, and also the vessels 

 which bring the blood from the intestines containing the 

 absorbed matter from the food, which the liver elaborates and 

 perfects. The liver is a blood-making organ, and it appears 

 also to form or secrete fatty matter. When the venous blood 



