196 BOARD OF AGRICULTURE. [Jan., 



microscope to our aid. By examining blood with this instrument 

 we find floating in its plasma, or fluid portion, a vast multitude of 

 blood cells, or globules; they are round, of a flattened shape like 

 a coin, and all biconcave. In diameter they vary from ^•g'o^ of an 

 inch to 4-^^, and all about y-^^^o of an inch in thickness; their 

 sacks or walls are elastic, which allows them to become elongated, 

 thus enabling them to pass through the difiicult passages of the 

 minute capillaries; they can also become biconcave, or even globu- 

 lar. We find them arranged one upon another, in a more or less 

 regular manner, and a few scattered about, presenting very much 

 the appearance of a roll of coin when carelessly dropped upon the 

 table, some still in position and a few scattered about. There are 

 other cells in the blood, but our purpose is not with them ; neither 

 is it pertinent to our question to inquire into the composition or 

 origin of these interesting bodies. I will call attention to them 

 only because of their office, which is in the direct line of our 

 inquiry, for they are the carriers of oxygen, absorbing it instantly 

 in the lungs, changing the color at once from blue to red, and by 

 its circulation carrying it to every portion of the body, where it is 

 consumed in the production of heat. 



Thus we see how the air that surrounds our world, colorless, 

 tasteless, and almost unappreciable to the senses of man, becomes 

 at once, when we study it, one of 'the most interesting and 

 important questions of natural science. "We have seen in the 

 composition of the air how necessary are each of its components 

 to the existence of both animal and vegetable life — how the inju- 

 rious qualities of them all are controlled by opposite ones found in 

 another. We have glanced at the structure of the organs of 

 respiration and at the circulation of the blood, and have endeavored 

 to trace how the fierce oxygen of the air is toned down and fitted 

 for respiration^ enters the blood and is carried to all parts of the 

 body, and there silently and quickly consumed. 



After this long preamble we come to the direct subject of this 

 paper. We cannot take up a subject at once and discuss it, per 

 se, without going back of it and looking at the conditions upon 

 which it depends, as we have in this case, which has, I trust, 

 enabled us to recognize the importance of a regular supply of pure 

 air, which is more necessary for the maintenance of the lives of 

 our domestic animals, or even man himself, than good food. We 



