THE BLOOD. 221 



and into the part previously expanded ; and by a continuance of this 

 process the whole mass makes a slow progression across the field of 

 the microscope. 



These movements are accomplished, like those of the amoeba, by local 

 contractions and relaxations of the substance of the globule. In Amoeba 

 princeps the movement of progression may take place at the rate of 73 

 micro-millimetres per minute, and in some gelatinous animalcules it is 

 so active that it may be followed continuously by the eye. But the 

 movement of the white globules of the blood is much more slowly 

 performed, and, like that of the hour-hand of a clock, is to be distin- 

 guished only by noting their change of position after a certain time. 

 The white globules of the frog, on the free surface of the mesentery, 

 may move at a rate, as measured by the micrometer, of 13 micro- 

 millimetres per minute', and similar granular corpuscles, in the con- 

 nective tissue of the mesentery, may progress at the rate of 3.5 micro- 

 millimetres in the same time. Certain cells in the frog's cornea, regarded 

 by some observers as identical with the white globules of the blood, 

 may change their position in the cornea at the rate of 2.5 micro-milli- 

 metres per minute. 



The amoeboid movement is sometimes, seen in the interior of the 

 capillary blood-vessels or small veins, when the globules are imprisoned 

 in a stagnant portion of the blood-plasma. But if the circulation be 

 reestablished, as the globules again move with the blood current, they 

 cease to be distorted, and resume their rounded form. 



The physiological properties and functions of the white corpuscles 

 are not so distinct as those of the red globules. Their great inferiority 

 in number shows that they are less important for the immediate con- 

 tinuance of the vital operations ; and the same thing may be inferred 

 from their want of strongly marked specific characters. For while the 

 red globules of the blood vary in appearance to a marked degree in dif- 

 ferent classes, orders, and families, the white globules present nearly 

 the same general features of size, form, and structure throughout the 

 series of vertebrate animals. 



Plasma of the Blood. 



The plasma is a transparent, colorless, homogeneous liquid, in which 

 the blood-globules are suspended. It consists of water, holding in solu- 

 tion mineral salts and albuminous matters, with various crystallizable 

 substances of organic origin. Its albuminous matters are the most 

 abundant and important of its solid ingredients. Its average compo- 

 sition, according to the most careful estimates, is as follows : 



COMPOSITION OF THE BLOOD-PLASMA. 



Water 902.00 



Albumen 53.00 



Paraglobuline 22.00 



Fibrinogen 3.00 



Patty matters 2.50 



