"A diseased pathological condition causes a diminution in the proportion of active principles of the nourishing fluid, and especially in fibrine, of which the abundance is allied to the most important activity of the vital work in some parts of the organism." "The blood," says Dr. Jones, "is not only distributed by innumerable channels through every recess of the body; the blood is not only the source of all the elements of structure; the blood not only furnishes the materials for all the secretions and excretions, and for all the chemical changes,--but the blood is in turn affected by the physical and chemical changes of every vessel, of every nerve, of every organ and texture of the body. It is evident then that the constitution of the blood will depend upon the food, upon the vigor and perfection of the organs of digestion, respiration, circulation, secretion, and excretion; upon the vigor and perfection of the nervous system, and of all the organs and apparatus; and upon the correlation of the physical, vital, and nervous forces. The character of the blood will then vary with the animal; with the organ and tissue through which it is circulating; with the age, sex, temperament, race, diet, previous habits, occupation, and previous diseases; with the soil and climate; and with the relative states of the activity of the forces." VII. Thus it appears how important is the function of respiration, and how vital the necessity for pure air. Pure dry air contains about 21 gallons of oxygen, and 79 gallons of nitrogen out of 100, and about one gallon of carbonic acid out of 2500. Man will consume, on the average of 20 respirations a minute, or 1200 respirations the hour, about 20 pounds of air, and give off 2-1/2 pounds or more of carbonic acid, besides half a pound of watery vapor, per diem, or, according to Andral and Gavaret, 22 quarts of carbonic acid per hour. We have shown in the chapter on Alimentation how this process of respiration affects the nutrition, and how serious the results of its disturbance. The purer the air, the more perfect the type of men and animals. This was understood by the ancients, and they established their most famous schools for gladiatorial training at Capua and Ravenna. The same law is observed at the present day by the admirers of the race-horse. The purity of the air gives purity to the blood, and the blood builds up the system in like proportion of excellence. VIII.