THE BLOOD AND ITS CIRCULATION 347 



" lymph " — is held in a closed system of vessels, and 

 does not receive any of the lymph. When examined 

 with the microscope, the blood, or haemolymph, of man 

 is found to consist of an albuminous, slightly sticky 

 liquid, in which float an immense number of " corpuscles " 

 — minute bodies, some rounded, some irregular, some 

 bun-like, and some spherical. The most abundant of 

 these are the " red corpuscles," of the shape of buns, 

 slightly depressed on each surface. Three thousand two 

 j hundred of them could be placed lying flat side by side 

 along the space of a measured inch. They appear pale 

 greenish-yellow in colour under the microscope, but in 

 quantity, lying one over the other, they allow only red 

 and some blue light to pass through them, and so have 

 a fine red colour. They consist of a small quantity of 

 albuminous matter and water, and of a large proportion 

 of a red-coloured, crystallizable, chemical substance dis- 

 solved in them, called haemoglobin, or blood-red. It is 

 this haemoglobin which performs one of the most im- 

 portant duties of the blood, since it combines with the 

 oxygen of the inspired air when the corpuscles are 

 flowing through the fine vessels of the lungs, and 

 carries it to the tissues in every part of the 

 body, which greedily take the oxygen from the red 

 corpuscles. 



The red corpuscles of man's blood and that of the 

 hairy suckling animals — the mammals — are not nucleated 

 cells, but are regularly formed and renewed as they daily 

 wear out, as fragments of larger mother-cells, which 

 break up into these corpuscles, in the marrow of the 

 bones, and some other situations where they are found. 

 In all other vertebrates the red blood corpuscles have a 

 kernel, or dense nucleus, and are complete " cells," 

 usually oval, smooth and .fattened in shape — a curious 



