THE BLOOD. Ill 



CHAPTER VII. 



OF THE BLOOD. 



The Offices and Relation of Blood in the System. The Plasma and Cells. General Properties 

 and Composition of the Blood. Quantity in the Body. Coagulation. Blood-cells. Their suc- 

 cessive Forms. TJie perfect Cell. Hcematin: its Properties. Number of Blood-cells. Plas- 

 ma : its Composition, and Variations of its Ingredients. Albumen, Fibrin, Fat, Sugar. Min- 

 eral Ingredients of the Cells and Plasma compared. Gases of the Blood. Changes occurring 

 during the Circulation. General Functions of the different Ingredients oftheBhod. Introduc- 

 tion of Oxygen by the Cells. Tlieir transient Duration. 



IT is necessary for the functional activity of every organized being that 

 there shall circulale-throjigh all parts of it a nutritive liquid. In plants, 

 it is the sap ; in animals, the blood. 



Since the life of plants manifests itself, for the most part, in a purely 

 formative result, and involves little or no destruction of parts, The blood: its 

 the circulating current is devoted almost entirely to nutrition, functions. 

 But in animals, whose conditions of existence involve extensive and un- 

 ceasing destruction, the current is burdened with another duty. It is 

 also the means of removal of dying or wasted portions. 



In the first chapter it was shown that about a ton and a half of mate- 

 rial is required by a man in the course of a year, and that in introduction 

 the same period a like amount is removed from the system, ^grki'bythe 

 When we reflect that the introduction and removal of this blood, 

 immense mass is accomplished through the agency of the circulating 

 blood, it is obvious that that fluid must be undergoing the most rapid 

 changes. The rapidity with which dying matters are removed is strik- 

 ingly illustrated by the minute extent to which they are permitted to ac- 

 cumulate in a healthy state. These elements of decay are strained off 

 or exhaled as quickly as they arise. That fancied power, the " vis med- 

 icatrix naturae," is only an ideal expression of the perfection with which 

 the various eliminating mechanisms work. Poisonous agents, whether 

 they have been introduced from without or have originated from morbid 

 actions within, like all other useless or noxious products, find their prop- 

 er channel of escape, and the system will thus rid itself of intoxicating 

 liquids and narcotic drugs if their quantity does not exceed the amount 

 that it can destroy or excrete in a special period of time. 



Considered in its relation to nutrition, the circulating liquid presents 

 many interesting aspects. Each of the thousand variously-constituted 

 parts of the body is withdrawing the supplies it needs : the muscular, the 



