V8 THE HORSE AXTJ ITS DISEASES. 



blood returning to the heart by the veins, which was 

 before supposed to flow from tlie heart by them, and 

 having once begun his researches, he did not leave them 

 till he gave us the true route and course of the fluid 

 through the body. 



The action of the air on the blood, we have every 

 reason to suppose, that the blood is constantly wasting, 

 for it tends to support the growth of parts ; admitting 

 this, it becomes necessary it should have sources of 

 renovation and restoration, which appear to be derived 

 from the lungs and the chylopoetic viscera. By the 

 first it is altered and meriorated, and by the latter it is 

 renovated in point of quantity. The blood seems to 

 acquire from the air a certain part, or possesses itself 

 of certain properties, whereby its qualities are brought 

 back from a venal to an arterial state, which is the only 

 one that seems fit for the purposes of support. When 

 the venal blood is exposed to the action of the air, it 

 soon loses its dark hue, and becomes florid and bright in 

 the part exposed to the atmosphere ; and as the other 

 portions are successively exposed, they become in the 

 same manner brilliant. 



If venal blood is also placed in a bladder, those parts 

 in contact with the bladder become brightened. If 

 blood in the pulmonary artery is examined, it will be 

 found dark, impure, and ^Tnous, when, on the contrary, 

 examined in the pulmonary vein, it will be found bright, 

 florid, and arterial. "We likewise observe, that the same 

 changes, as far as regards color, take place in the blood 

 in its passage through the lungs, by means of its 

 exposure to the action of the air in the bronchial tubes 

 or cells. That this arises from the air we know, for if 

 we hang or strangle any animal, and then open each 

 side of the heart, we shall find the blood in both equally 

 black and venous. It is also certain that the change of 

 color is not the only alteration that the blood receives, 

 otherwise it would be a change on the least useful part 

 of the blood ; but it is more probable that it is an effect 



