THE DISEASES OF CATTLE. 67 



illustration. Water seems to be almost as essential for the pur- 

 poses of respiration as that of nutrition ; and when we realize 

 the fact, that the animal frame is composed of 75 per cent of 

 water ; that three -fourths of the wondrous and complicated 

 mechanism of man and his congeneric flocks and herds is com- 

 posed of the " dew-drops ;" that the vital current which courses 

 the arteries of each, and gives vitality, health, and beauty to 

 the animal mechanism, is in the same ratio, we must come 

 to the conclusion that water plays a very essential part in the 

 animal economy, both as regards respiration and nutrition. 



Chemistry has demonstrated that 'pure air, which I contend 

 is absolutely necessary for the purpose of physiological respira- 

 tion, is not composed of a single element, as some suppose, but 

 is a unity of three gases, termed oxygen, nitrogen, and carbonic 

 acid. These unite in the following equivalents : Oxygen, 21 

 per cent ; nitrogen, 75 p.er cent ; carbonic acid, one per cent. 

 These equivalents are persistent ; they never unite in any other 

 form ; hence we know, from inductive evidence, that the ele- 

 mentary basis of a pure atmosphere rests on the above propo- 

 sition, so that the elementary constituents of pure air are the 

 same all over the world. 



Oxygen. — This gas does not exist in a free state, but in com- 

 bination, it is universally dispersed throughout nature. It unites 

 with light and heat, as well as air, and to bodies in a state of 

 combustion, and so intense is its own caloric power, that if it 

 could be set free throughout nature, a universal conflagration 

 might be expected ; the hardest rocks w^ould crumble to dust, 

 and even the diamond, considered as indestructible, would melt 

 as with " fervent heat." This gas has neither taste nor odor, 

 and like common air is capable of indefinite expansion and 

 compression. It is indispensable to respiration, and generates 

 animal heat. 



The estimated weight of oxygen respired by a healthy man 

 in 24 hours, is 2 1-4 pounds. This, in a gaseous state, occupies 

 a volume of 48,000 cubic inches. It unites with the carbon of, 

 the blood, and in the course of 24 hours liberates from the lungs 

 48,000 cubic inches of carbonic acid jras. 



