BLOOD. 41 



2. The Fats are absorbed by the lacteals, emptied into the thoracic duct, 

 and enter the blood at the junction of the internal jugular and subclavian 

 veins. 



Forces aiding the movements of Lymph and Chyle. 



1. Endosmosis. The continued transudation of matter from the capil- 

 laries, and its absorption into the lymphatics by endosmosis, constitutes the 

 main cause, the vis-a-tergo y of the movement of the lymph ; it is so con- 

 siderable as to rupture the walls of the vessels if they are ligated. 



2. Contraction of the non-striated muscular fibres in the walls of the 

 lymphatic vessels, especially when fully distended, aided by the action of 

 the valves, promotes the onward flow of the fluids. 



3. Muscular contraction in all parts of the body, by exerting intermit- 

 tent pressure upon the lymphatic vessels, hastens the current onward ; 

 regurgitation being prevented by the closure of the valves. 



4. The inspiratory movement, by expanding the chest, causes a dilation 

 of the thoracic duct, and a rapid flow of lymph and chyle into it ; during 

 expiration it is compressed, and the fluids forcibly expelled into the venous 

 system. 



BLOOD. 



The Blood is a nutritive fluid containing all the elements necessary for 

 the repair of the tissues ; it also contains principles of waste absorbed from 

 the tissues, which are conveyed to the various excretory organs and by them 

 eliminated from the body. 



The total amount of blood in the body is estimated to be about one- 

 eighth of the body weight; from 16 to 18 pounds in an individual of aver- 

 age physical development. The quantity varies during the 24 hours ; the 

 maximum being reached in the afternoon, the minimum in the early 

 morning hours. 



Blood is a heterogeneous, opaque red fluid, having an alkaline reaction, 

 a saline taste, and a specific gravity of 1.055. 



The opacity is due to the refraction of the rays of light by the elements 



which the blood is composed. The color varies in hue, from a bright 

 :arlet in the arteries to a deep purple in the veins, due to the presence of 



coloring matter, hemoglobin, in different degrees of oxidation. 



The alkalinity is constant, and depends upon the presence of the alka- 



ie sodium phosphate, Na 2 H PO 4 . 



The saline taste is due to the amount of sodium chloride present. 



The specific gravity ranges within the limits of health, from 1.045 to 

 1.075. 



D 



