THE SMITHSONIAN INSTITUTION. 147 



them at all points, allow tlie destroy ei* freer access to every part of 

 their tissues. 



Were it not for this dissolving agency of oxygen, the earth would 

 be everywhere strewn with the undecaying remains of plants and 

 animals. Tliese, accumulating generation after generation, would en- 

 cumber its surface, until at length it would become one great charnel- 

 house filled with the unburied dead. 



Oxygen thus performs the part of an undertaker. It removes the 

 dead out of our sight. And as in the case of the human undertaker, 

 the graves to which it consigns the lifeless forms intrusted to it, are 

 not eternal. They, too, give up their dead. The elements of the de- 

 caying tree, plant and animal, although for a time lost to our sight, 

 at length reappear in new organic forms, clothed with fresh life and 

 beauty. 



Of the same nature is the office performed by oxygen in respiration. 

 Penetrating with the blood all parts of the body, it passes by the 

 living, but everywhere attacks the dead cells and prepares them for 

 removal from the system. It is only by oxydation that the material 

 of these cells becomes soluble, and it is only in a state of solution that 

 they can be borne out of the living organism. Every breath is 

 freighted with exhalations from the funeral pyres of unnumbered 

 corpses. 



In this oxydation of tissue, which is constantly going forward, cer-, 

 tain imponderable agents or forces indispensable to the living functions 

 are liberated. In every part -of the body heat is evolved, and in the 

 brain, that more subtle fluid, which directed along the different ner- 

 vous channels, controls the movements of the entire frame. The 

 true source of animal motive power is not to be sought in the endow- 

 ments of spirit. This merely directs, it does not originate it. Voli- 

 tion is the touch of the key by the operator of the telegraph. UnlesS' 

 supplied with the requisite force by the brain, the will might as easily 

 create an arm as move it. As in the steam-engine and the electro- 

 magnetic engine, so in the animal organism oxydation is the trut 

 source of the power generated. 



The nitrogen of the atmosphere is a mere diluent of the oxygen. 

 It takes no part in any of the work performed by the latter. Nay, 

 it stands in the way of the latter, and by its physical presence hin- 

 ders its activities. This is, indeed, its intended office and function. 

 Did oxygen compose the entire atmosphere, bodies coming in contact 

 with it at points five times more numerous than they now do, would 

 waste away too rapidly under its action. By the interposition of the 

 nitrogen its activities are kept within the j)roper limits, while at the 

 same time the atmosphere has the weight and density necessary for 

 its mechanical functions. 



Those oxydizing processes so universally in progress would soon 

 cease from the exhaustion of subjects, were there no provisions in na- 

 ture for their continued supply. Such provisions, however, are found 

 in the vegetable organism. In the leaves of plants while under the 

 influence of the sun's rays, water and carbonic acid, the sulphates 

 and the phosphates, undergo re-solution. The greater part of the 

 oxygen is thrown off, while the hydrogen, carbon, sulphur, and phos- 



