238 THE PRINCIPLES OF AGRICULTURE 



fail to fulfill their function to any degree, every organ and 

 function is affected. Most of the waste nitrogenous matter 

 leaves the body through the kidneys, but if this channel of 

 elimination is interfered with, the effete matters are retained, and 

 they poison and derange every organ from the brain downward. 

 Even apparently insignificant organs have a far-reaching in- 

 fluence. The spleen and bone marrow-cells affect the develop- 

 ment of blood globules. A small gland at the throat (thyroid) 

 affects the nervous system, and a still smaller one at the base 

 of the brain (pituitary) influences the growth of the limbs. 



411a. Repeat the experiment suggested in 390a. Make lime 

 water by placing a piece of quicklime in a bottle of pure 

 water, shaking and setting aside to settle. Then take a little 

 of the clear liquid and with a syringe force air through 

 it. It will become only slightly turbid. Next take a tube and 

 blow through this water for a short time, when it will become 

 white and opaque by the formation of lime carbonate, owing 

 to the union of carbon dioxid with the lime. 



413a. The lung of any of the higher animals presents an 

 enormous surface to the inspired air. To illustrate the extra- 

 ordinary extent of breathing surface formed by this minute di- 

 vision of the lungs into microscopic sacs, it may be stated that, 

 in the horse, it reaches an area of 500 to 800 square feet. 



414a. The heart of an ox, sheep, or other animal can be 

 obtained at the slaughter house or of the butcher. Discover 

 the right and left cavities, a ventricle surmounted by an auricle 

 on each side, the valves around the opening leading from the 

 auricle to the ventricle, and the cords connecting the valves with 

 the inner side of the ventricle. 



416a When blood is shed in killing an animal or otherwise, 

 observe how the surface layer gradually changes from the dark 

 red to a bright crimson as it takes up the oxygen from the air. 



418a. In the conveyance of oxygen in the blood the color- 

 ing matter of the red globules (hemoglobin) is the principle 

 bearer. It combines with oxygen loosely, and gives it up promptly 

 at the demand of the carbon. The bright crimson color is due 

 to the union of much oxygen with the coloring matter of the 



