444 OF NUTRITION. 



tion " extractive matter." Its Specific Gravity may be stated at about 1030 

 in health; and it contains about 9^ per cent, of solid matter. When it is 

 heated to 160, its Albumen coagulates and the remaining fluid may be sepa- 

 rated by pressure. This fluid still contains some Albumen, which is held in 

 solution by free alkali ; for if the latter be neutralized by Acetic acid, a further 

 precipitation takes place on the application of heat. The fatty matter, which 

 may be separated by ether, seems to be nearly allied to the several fatty sub- 

 stances formed in the body ; for some chemists have determined it to consist 

 of Oleine, Margarine, and Stearine, the constituents of ordinary fat ; whilst others 

 regard it as analogous to Cerebrine, the fatty matter of the brain ; and others, 

 again, consider it to bear a closer resemblance to Cholesterine, the fatty matter 

 of the bile. The Extractive, matter partly consists of Lactic acid, partly of a 

 substance called Osmazome ; it is believed by Berzelius that this portion of 

 the blood contains the resultants of the acts of decomposition continually taking 

 place in the body ; and that it is chiefly, therefore, from this that the excre- 

 tions are formed. 



587. It cannot be doubted that, upon the due admixture in the Blood of all 

 these elements, the regular performance of its actions is dependent. In regard 

 to its physical properties merely, it is easily shown that a slight alteration may 

 produce the most injurious consequences ; for a certain degree of viscidity has 

 been found (by the experiments of Poisseuille) to favour the passage of fluid 

 through capillary tubes; and thus, if the viscidity of the blood be diminished 

 by a loss of part of its Fibrin, stagnation of the current, and extravasation of 

 a portion of the contents of the vessels, will be the result. This has been 

 fully proved by the numerous experiments of Magendie ; and the fact is one 

 of very important Pathological applications ( 592 6). In regard to the effect 

 of alterations in the amount of the Red Particles, our information is less satis- 

 factory, since it is almost impossible to deprive Blood of these, without at the 

 same time defibrinizing it. It appears, however, from the experiments of 

 Dieffenbach on transfusion, that they are more effectual as stimuli to the 

 Heart's action, than is any other constituent of the blood ; and, if the hypo- 

 thetical account of their use already offered ( 576) have any correctness, they 

 must be important agents in the maintenance of the Capillary Circulation also. 

 The rapidity with which they may be decomposed and reconstituted, is made 

 remarkably evident by the experiments of Magendie, who found that, when 

 the Blood of one animal was injected into the veins of another having discs of 

 very different size and form (care being taken to prevent the coagulation of 

 the Fibrin during the operation), the original Red particles soon disappeared, 

 and were replaced by those characteristic of the species, in whose veins the 

 fluid was circulating. The Albumen of the Blood seems to be chiefly of im- 

 portance as the material from which Fibrin is elaborated. The continual 

 drain upon the Fibrin, which is taking place in the capillaries of the system, 

 is made evident by the remarkable fact, that Arterial blood contains a much 

 larger proportion of it than Venous, the excess being usually about one-fifth. 



588. The Crassamentum not unfrequently exhibits, in certain disordered 

 conditions of the Blood, a layer of Fibrin nearly free from colour; and this is 

 known as the Buffy coat. The presence of this has been frequently regarded 

 as a sign of the existence of Inflammation, occasioning an undue predominance 

 of Fibrin ; but this idea is far from being correct, since, as will presently 

 appear, (589), it may result from a very opposite condition of the Blood. A 

 similar colourless layer of Fibrin is always observable, when the Coagulation 

 of the blood is retarded by the addition of agents that have the power of delay- 

 ing it ( 582) ; and since, in Inflammatory states of the system, the blood is 

 generally long in coagulating, it has been supposed that the separation of the 



