136 ANATOMY AND PHYSIOLOGY. 



about fourteen or fifteen per cent, by weight of the whole mass, in 

 man twelve or thirteen per cent., and both of these are warm- 

 blooded animals. The red globules in fishes (which are cold- 

 blooded, or only slightly warmer than the water in which they live) 

 amount to about five or six per cent. It is also stated that these 

 globules are in general more numerous in the blood of men than in 

 that of females, and in persons of a sanguine than in those of a 

 lymphatic temperament. 



One of the most singular properties of blood, is its power of co- 

 agulating. It has been supposed that the globules of blood are 

 really vesicles or bags, the outer portion of which is composed of red 

 coloring matter, while the centre consists of fibrin ; and that, during 

 coagulation, the vesicle is burst, and the particles of fibrin adhere 

 to each other. But it has been more recently shown, by the ex- 

 periments of Babington and Miiller, that the fibrin is riot contained 

 in the red globules, but in the fluid part of the blood in which they 

 float. When inflammation exists, the separation of the two parts 

 is most complete, the yellow or upper buffy layer being the fibrin. 

 Much beautiful design, as Dr. Prout remarks, is probably concealed 

 under this arrangement. One object of it is evident. If the blood 

 did not coagulate, the existence of animals would be most precari- 

 ous, as, on the slightest injury, they would be liable to bleed to 

 death. 



There must, therefore, evidently be a cause for the fluidity of the 

 blood within the body, and many experiments render it highly pr< 

 bable that this depends, to a certain extent at least, upon the vital- 

 ity of the veins and arteries circulating it. Even the vitality of 

 the blood itself is made more than probable by the experiments of 

 Mr. John Hunter. Like the egg, it can, within certain limits, resist 

 the influence of various agents, such as heat and cold, while it 

 retains life, but yields to them when it dies. An electric shock 

 passed through it, instantly extinguishes its vitality, and this is the 

 reason why the blood in persons struck dead by lightning is always 

 fluid. 



While physiologists had yet but inaccurate ideas of the uses and 

 structure of different organs, great benefits it was thought might 

 follow from transfusing a healthy animal's blood into a diseased 

 person's body, and some dangerous and even fatal experiments of 

 this kind were performed in France, until the practice was inter- 

 dicted by law. Of late years the practice has been revived, in cases 

 where great loss of blood has happened, and its previous failure has 



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