22 THE BLOOD. 



genie matter are derived in part from the food and in part from the liver, where sugar 

 and glycogenic matter are manufactured. They are of organic origin, definite chemical 

 composition, and crystallizable. The fats and sugars are distinguished from other or- 

 ganic principles by the fact that they are composed of carbon, hydrogen, and oxygen. 

 In the sugars, the hydrogen and oxygen exist in the proportion to form water, which 

 fact has given them the name of hydrocarbons or hydrates of carbon. The principles 

 of this class play an important part in development and nutrition. . One of them, sugar, 

 appears very early in foetal life, formed first by the placenta, and afterward by the liver, 

 its formation by tm3 latter organ continuing during life. Fat is a necessary element of 

 food, and is also formed in the interior of the body. The exact influence which these 

 substances have on development and nutrition is not known; but experiments and obser- 

 vation have shown that this influence is important. They will be considered more fully 

 under the head of nutrition. 



4. Excrementitious Matters. A full consideration of these principles, which are all 

 formed by the process of disassimilation of the tissues and are taken up by the blood to 

 be eliminated by the proper organs, belongs to excretion. The relations of carbonic 

 acid to the system will be fully considered in connection with respiration. 



5. Organic Nitrogenized Principles. This class of proximate principles is of organic 

 origin, indefinite chemical composition, and non-crystallizable. Substances forming this 

 class are apparently the only principles which are endowed 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 differ- 

 ent from any thing which is 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 trans- 

 formed 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 with- 

 out undergoing any change. The analogous substances which exist in food undergo a 

 very 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, semisolids, and fluids of the body, never alone, but 

 always combined with inorganic substances. As a peculiarity of chemical constitution, 

 they all contain nitrogen, which has given them the name of nitrogenized or azotized 

 principles. In studying their properties more fully, we shall see that they are by far the 

 most important elements in the organism. The elaborate preparation which they require 

 for absorption involves the most important part of the function of digestion. Their ab- 

 solute integrity is necessary to the operation of the essential functions of many tissues, 

 as muscular contraction or conduction of nervous force. An exact knowledge of all 

 the transformations which take place in their regeneration and the process by which 

 they are converted into effete or excrementitious matters would enable us to comprehend 

 nutrition, which is the most important part of physiology ; but as yet we know little of 

 these changes, and may consider ourselves fortunate in understanding a few of the laws 

 in accordance with which they are regulated. 



Of the different classes of proximate principles existing in the blood, it is at once 

 apparent that the organic nitrogenized principles are more complex in their constitution, 

 properties, and functions than the other classes. These principles, as they exist in the 

 blood, possess peculiar and characteristic properties, which it will be necessary to study 

 in detail. 



Plasmine, Fibrin, Hetalbumen, Serine. The name plasmine was given by Denis to a 

 peculiar principle 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-sev- 

 enth part of its volume of a concentrated solution of sulphate of soda, which prevents 

 coagulation ; in a short time the corpuscles gravitate to the bottom of the vessel, and 



