OF THE BLOOD. 45 



chyle thus formed is conveyed into the left subclavian vein 

 (Fig. 3). 



76. When an animal has been kept without food for 

 some time, these vessels are nearly empty ; but when diges- 

 tion is going on rapidly they become filled with chyle, the 

 colour of which is white, like milk ; and hence the name of 

 lacteals given to them by their discoverers. 



The absorption of the chyle seems to take place chiefly by 

 means of the villosities ; for so soon as this phenomenon com- 

 mences, they become swollen, like sponges filled with milk by 

 imbibition. From these the chyle passes into the lymphatic 

 (lacteal) vessels, by a process as yet unknown ; and after 

 traversing the mesenteric glands, proceeds by other lacteals 

 from these glands to the thoracic duct. The cause of this 

 iipward and onward movement of the chyle towards the 

 veins is not well known. 



77. Chyle. This liquid varies in appearance according 

 to the animal and the kind of food which has been used. In 

 man and in most mammals it is of a milky- white colour, of a 

 peculiar odour and brinish alkaline taste. Examined by the 

 microscope, it seems composed of a serous liquid, holding in 

 suspension fatty drops and circular globules. Chyle formed 

 from food not including fatty matters is much less opaque 

 than that having in its composition oil and fat. In birds, 

 the chyle is almost always transparent. 



Taken from the lacteals near their origin in the intestines, 

 the chyle is found to be composed mostly of albuminous 

 matters; but examined in the thoracic duct, near its junction 

 with the subclavian vein, it is found to contain fibrin, in- 

 creasing in quantity the nearer to its passage into the venous 

 blood. On the presence of this substance depends its property 

 of spontaneous coagulation, like the blood. It now becomes 

 of a light rose-colour, and reddens slightly on exposure to 

 the air. In brief, it more and more resembles the blood, with 

 which it finally mingles in the left subclavian vein. 



We have traced the elaborated nutritive matter to the 

 blood. This fluid must now engage our attention, also the 

 manner in which it is distributed to all parts of the body. 



OF THE BLOOD. 



78. In animals of the simplest structure, all the liquids 

 of the animal economy resemble each other. It seems, in- 



