12 



THE ESSENTIALS OF HISTOLOGY. 



The coloured blood-corpuscles. Under the microscope the blood is 

 seen to consist of a clear fluid (plasma), in which are suspended the 

 blood-corpuscles. The latter are of two kinds : the red or coloured (fig. 8, 

 r, r), which are by far the most numerous, and the white, pale, or 

 colourless (p, g), which from their occurrence in the lymph are also 

 known as lymph-cwpuscles. When seen singly the coloured corpuscles 

 are not distinctly red, but appear of a reddish-yellow tinge. In the 

 blood of man and of all other mammals, except the Camelidae, they 

 are biconcave circular disks. Their central part usually has a lightly 

 shaded aspect, under the ordinary high power (fig. 9, 1), but this is due 

 to their biconcave shape, not to the presence of a nucleus. They have 

 a strong tendency to become aggregated into rouleaux and clumps 

 when the blood is at rest, but if it is disturbed they readily become 

 separated. 



If the density of the plasma is increased in any way, as by evapora- 

 tion, many of the red corpuscles become shrunken or crenated (c). 



The average diameter of the human red corpuscles is 0'0075 milli- 

 meter (about ^Vir inch). 1 



There are from four to five millions of coloured corpuscles in a cubic 

 millimeter of blood. 



The colourless corpuscles of human blood are protoplasmic cells, 

 averaging 0*01 mm. (^-Vo^ i ncn ) in diameter when spheroidal, but they 



vary much in size. They are far 

 fewer than the coloured corpuscles, 

 usually numbering not more than 

 ten thousand in a cubic millimeter. 

 Moreover, they are specifically 

 lighter, and tend to come to the 

 surface of the preparation. If ex- 

 amined immediately the blood is 

 drawn, they are spheroidal in shape, 

 but they soon become irregular 

 FIG. 10. FIBRIN-FILAMENTS AND BLOOD- (fig. 8, p, g), and their outline con- 

 TABLETS. tinually alters, owing to the amboea- 



A, network of fibrin, shown after washing away ..... .. _ , . , , 



the corpuscles from a preparation of blood like changes 01 lOrni to Which they 

 that has been allowed to clot ; many of the , . A , , , 



filaments radiate from small clumps of blood- are SUDJCCt. bome OI the COlOUriCSS 

 tablets. B (from Osier), blood-corpuscles and -, j ~ ' -. 



elementary particles or blood-tablets, within Corpuscles are Very pale and finely 



granular, others contain coarser and 

 more distinct granules in their protoplasm. The protoplasm may also 



1 The following list gives the diameter in parts of -A millimeter of the red blood- 

 corpuscles of some of the common domestic animals: Dog, 0'0073; rabbit, 0'0069; 

 cat, 0-0065 ; sheep, 0'0050 ; goat, 0'0041. 



