SECTION Y. 



The Fluids carrying Nourishment to the Tissues 



BLOOD AND LYMPH. 



The blood carries the necessary nourishment to the tissues, 

 and receives their waste products. But it is enclosed in a 

 closed system of vessels, and does not come into direct 

 relationship with the cells. Outside the blood-vessels, and 

 bathing the cells, is the lymph which plays the part of 

 middleman between the blood and the tissues, receiving 

 nourishment from the former for the latter, and passing the 

 waste from the latter into the former. 



A. BLOOD. 



The iihysical, chemical and histological characters of 

 blood must he investigated 'practically. 



I. General Characters. 



Colour. — Blood, when it has stood for some time, is dark 

 purple, but when shaken with air it assumes a bright 

 cinnabar red colour. Elements of Blood. — Microscopic 

 examination shows that blood is composed of a clear fluid 

 (Liquor Sanguinis or Plasma) in which float myriads of 

 small disc-like yellowish-red cells (Erythrocytes), a smaller 

 number of greyish cells (Leucocytes), and certain very minute 

 grey particles (Blood Platelets). The Opacity of Blood is due 

 to the erythrocytes, and, when the pigment is dissolved out 

 of them by water and they are rendered transparent, the 

 blood as a whole becomes transparent and is said to be 

 "laked" (p. 485). The Specific Gravity is about 10-55. It 



474 



