The influence of the degeneracy of the fluids in diseases has no doubt been exaggerated; too frequent a source of morbid derangements has been placed in this portion of the economy. But it cannot be denied, that according to the different alterations that the fluids exhibit, they may be capable of exciting differently the solids that contain them. We know that in the same individual, and with the same mass of aliments, digestion varies from one day to another in the duration of its periods; that some aliments prolong and others accelerate it; that some remain very long in the stomach, as it is said, and others as it were only pass through it. Now in all these cases the organ remains the same, the fluid only varies. According as the kidney secretes urine more or less acrid and consequently more or less irritating, the bladder retains it for a longer or shorter time. Such is oftentimes its stimulating qualities, that the moment it comes into this organ it is involuntarily rejected. Shall I speak of emetics and evacuants by the intestinal canal, the effects of which are so variable? We know that the words drastic, purgative, laxative, &c. indicate the different degrees of the stimulating qualities which certain substances introduced into the alimentary canal exhibit, degrees which are to be considered abstractedly from those of the sensibility of the organs; this in fact can be such, that a laxative may produce greater effects than a drastic purge. Not only the quality, but also the quantity of the fluids contained in the organic muscles, has an influence upon their contractility. 1st. The word plethora is certainly employed too loosely in medicine; but we cannot doubt that the state which it expresses sometimes exists; now the more blood there is in the heart, the more are its contractions accelerated. 2d. I have many times made transfusion in dogs, whether with a view to that alone, or in researches relative to respiration and circulation. Now I have always observed, that by not opening a vein, to empty the blood as fast as the external jugular receives it (for I always choose this vein for the experiment) by thus producing consequently an artificial plethora, I have, I say, always observed that the motion of the heart was accelerated. I have even seen the eye of a dog become bright and as it were inflamed; in others this phenomenon has not been observed. 3d. We know that in running, in which all the muscles by contracting press out from all sides the venous blood contained in their texture, this which enters the heart in abundance, makes it palpitate powerfully. 4th. There is not doubt but that the quantity of urine and excrements as much and more than their quality, is for the bladder and the rectum, a cause of involuntary contraction. 5th. We know the serious consequences that arise from giving emetics and cathartics in too large doses. 6th. A glass of tepid water often does not produce vomiting when a pint will bring it on powerfully, &c.