36 PHYSIOLOGY. 



animals : probably this arises from the fact that the latter 

 absorb less oxygen. If the blood of one animal be trans- 

 fused into another, it will frequently cause death. 



When blood stands for a time after being drawn, it sepa- 

 rates into two parts. One is called serum, and resembles the 

 white of an egg ; the other is the clot or crassamentum, and 

 forms the red coagulum, or jelly-like substance : this is ac- 

 companied by whitish, tough threads, called fibrine. When 

 blood has been drawn from a horse, and it assumes a cupped 

 or hollow form, if serum, or buffy coat, remain on its sur- 

 face, it denotes an impoverished state ; but if the whole, 

 when coagulated, be of one uniform mass, it indicates a 

 healthy state of this fluid. The blood of a young horse 

 generally coagulates into a firm mass, while that of an old or 

 debilitated one is generally less dense, and more easily divided 

 or broken down. The power that propels the blood into the 

 different ramifications of the animal, is a mechanico-vital 

 power, and is accomplished through the medium of the heart, 

 which is a powerful muscular organ contained in the chest. 

 From certain parts of it arteries arise ; in others the veins ter- 

 minate ; and it is principally by its alternate contractions and 

 expansions, aided, as already stated, by the vital power, that 

 the circulation of the blood is carried on. The heart is in- 

 vested with a membranous bag, called pericardium, which 

 adheres to the tendinous centre of the diaphragm, and to the 

 great vessels at the base of the heart. The heart is lubricated 

 by a serous fluid within the pericardium, which guards against 

 friction. In dropsical affections, the quantity of this fluid is 

 considerably increased, and constitutes a disease called dropsy 

 of the heart. The heart is divided into four cavities, viz., 

 two auricles, named from their resemblance to an ear, and 

 two ventricles, (as seen in plate 3, a b,) forming the body. 

 The left ventricle is smaller than the right ; but its sides are 

 much thicker and stronger : it is from this part that the grand 

 trunk of the arteries proceeds, called the great aorta, (i. e., /, 

 plate 3.) The right cavity, or ventricle, is the receptacle for 

 the blood that is brought back by the veins after going the 



