44 THE HUMAN BODY. 



the larger blood-vessels near where these empty into the 

 heart; by this flow of the lymph, under pressure from behind, 

 it is renewed in various organs, fresh liquid filtering through 

 the capillaries to take its place as fast as the old is carried off. 



The Lacteals. Jn the walls of the alimentary canal cer- 

 tain food-materials after passing through the receptive cells 

 into the lymph are not transferred locally, like the rest, by 

 dialysis into the blood, but are carried off bodily in the lymph- 

 vessels and poured into the veins of a distant part of the 

 Body. The lymphatic vessels concerned in this work, being 

 frequently filled with a white liquid during digestion, are 

 called the milky or lacteal vessels. 



Summary. To sum up: the blood and lymph form the 

 internal medium in which the tissues of the Body live; the 

 lymph is primarily derived from the blood and forms the im- 

 mediate plasma for the great majority of the living cells of 

 the Body; and the excess of it is finally returned to the 

 blood. The lymph moves but slowly, but is constantly reno- 

 vated by the blood, which is kept in rapid movement, and 

 which, besides containing a store of new food-matters for the 

 lymph, carries off the wastes which the various cells have 

 poured into the latter, and thus is also a sort of sewage stream 

 into which the wastes of the whole Body are primarily col- 

 lected. 



Microscopic Characters of Blood. If a finger be pricked, 

 and the drop of blood flowing out be spread on a glass slide, 

 covered, protected from evaporation, and examined with a 

 microscope magnifying about 400 diameters, it will be seen 

 to consist of innumerable solid bodies floating in a liquid. 

 The solid bodies are the blood-corpuscles, and the liquid is 

 the blood-plasma or liquor sanguinis. 



The corpuscles are not all alike. While currents still exist 

 in the freshly-spread drop of blood, the great majority of 

 them are readily carried to and fro; but a certain number 

 more commonly stick to the glass and remain in one place. 

 The former are the red, the latter the pale or colorless blood- 

 corpuscles. 



Red Corpuscles. Form and Size. The red corpuscles 

 as they float about frequently seem to vary in form, but by ^ 

 little attention it can be made out that this appearance is due 

 to their turning round as they float, and so presenting differ- 

 ent aspects to view; just as a silver dollar presents a different 



