We now see the close connection existing between the digestive system and the circulatory system. The digested food in the intestines is gathered in by villi cells. The question can now be asked, What do these cells do with this nutriment or digested food? They pour it into the absorbent vessels or lymphs, as they are called; these in turn empty the assimilated stores of food into larger and still larger vessels, which continues until the whole of the nutritive fluid is collected into one great duct or tube, which pours its contents into the large veins at the base of the neck, from whence it is carried into the circulatory system, the very basis of which is the blood.
The dark and impure blood, after returning to the heart, is sent to the lungs. It is, when collected from the body, just before being sent to the lungs dark, dull and loaded with worn-out matter. It must now be sent to the lungs, where it may be spread over the delicate thin walls of millions of vesicles, to be exposed to the air, which is inhaled by the acts of breathing. The blood gives off the broken-down material and carbonic acid gas very readily. It is both unpleasant and disagreeable, and the blood cells find it very unattractive.
The cells of the blood, however, have a great attraction for oxygen, consequently the cells absorb oxygen with greediness, so that when the blood returns to the heart it is fresh and bright and ready to take its journey back over the body again. This is done just about every three minutes. This endless round continues until stopped forever by death.
The relation existing between the animal and plant functions is brought to light in another way. When the plant was building tissue it released oxygen and exhaled it into the air. At the same time, by means of leaves, it gathered in the carbonic acid to use in plant building. Of course this was got from the air. The animal in performing its functions and in building its tissue inhales oxygen from and exhales carbonic acid gas into the air. Thus it is that animals take up what is unnecessary to the plant and the plant uses what is waste and poison to the animal.
When a colt is born the first and second temporary molars, three on each jaw, are to be seen. These are large when compared with the size of those that later replace them. In from five to ten days after birth the two central incisors or nippers make their appearance. In three or four weeks the third temporary molars appear, followed within a couple of months by an additional incisor on each side of the first two, both above and below. The corner incisors appear between the ninth and twelfth months after birth. This makes the full set of teeth--twenty-four in number.