22 THE BLOOD. 



longs to the physiology of excretion. The relations of carbon dioxide to the 

 system will be fully considered in connection with the physiology of res- 

 piration. 



5. Organic Nitrogenized Constituents. This class of constituents is of 

 organic origin, indefinite chemical composition and non-crystallizable. The 

 constituents included in this class are apparently the only matters that are en- 

 dowed with so-called vital properties, taking materials for their regeneration 

 from the nutritive fluids and appropriating them to form part of their own 

 substance. Considered from this point of view, they are different from any 

 substances met with out of the living body. They are all, in the body, 

 in a state of continual change, wearing out and becoming effete, when they 

 are transformed into excrementitious substances. The process of repair in 

 this instance is not the same as in inorganic substances, which enter and are 

 discharged from the body without undergoing any change. The analogous 

 substances which exist in food undergo elaborate preparation by digestion, 

 before they can even be absorbed by the blood-vessels; and still another 

 change takes place when they are appropriated by the various tissues. They 

 exist in all the solids, semi-solids and fluids of the body, never alone, but al- 

 ways combined with inorganic substances. As a peculiarity of chemical con- 

 stitution, they all contain nitrogen, which has given them the name of 

 nitrogenized or azotized matters. 



Of the different classes of constituents of the blood, it is at once apparent 

 that the organic nitrogenized matters are more complex in their constitution, 

 properties and uses than the other classes. These substances, as they exist in 

 the blood, possess certain peculiar and characteristic properties. 



Plasmine^ Fibrin, Metalbumin, Serine. The name plasmine was given 

 by Denis to a substance which he extracted from the blood by the following 

 process : The blood drawn directly from an artery or vein is received into a 

 vessel containing one-seventh part of its volume of a concentrated solution of 

 sodium sulphate, which' prevents coagulation ; in a short time the corpuscles 

 gravitate to the bottom of the vessel, and the plasma may be separated by 

 decantation ; to the plasma is added an excess of pulverized sodium chloride, 

 when a soft, pulpy substance is precipitated, which is plasmine. This sub- 

 stance, after desiccation, bears a proportion of about twenty-five parts per 

 thousand of blood. It is soluble in ten to twenty parts of water, when 

 a portion of it coagulates and may be removed by stirring with twigs or a 

 bundle of broom-corn, in the way in which fibrin is separated from the blood. 

 The fibrin thus separated is called by Denis concrete fibrin, and the substance 

 which remains in solution, dissolved fibrin. By most writers of the present 

 day, the dissolved fibrin of Denis is called metalbumin. 



According to Denis, plasmine is a proper constituent of the blood, and 

 after extraction by the process just described, it is decomposed into concrete 

 fibrin and dissolved fibrin, or metalbumin. Having removed the concrete 

 fibrin from the solution of plasmine, the metalbumin is coagulated by the 

 addition of magnesium sulphate, which does not coagulate ordinary albumin. 

 The proportion of dried metalbumin in the blood is about twenty-two parts 



