CLASSIFICATION OF THE TISSUES. 



21 



E. Compound tissues : 16. Vessels; 17. Glandular tissue ; 

 and 18. Nerve tissue. 



We shall, therefore, proceed in this manner, and turn first 

 to the blood. 



" Blood is quite a peculiar sort of juice," Goethe lets his 

 Mephistopheles say. Modern science, after nearly a hundred 

 years, endorses the apothegm completely. 



If a little drop of this fluid, which appears homogeneous to 

 the naked eye, is spread out in a thin layer under the micro- 

 scope, we are surprised by a peculiar image. The homoge- 

 neous red has disappeared ; we perceive innumerable yellow- 

 colored cells in a colorless fluid. The fluid is called plasma, 

 the cells bear the name of the colored or red blood corpuscles 

 (Fig. 10, a, b, c). Among the colored companions, still 

 another, though not abundant, colorless structure may be 

 noticed by closer examination. This is the lymphoid cell of 

 the blood, the so-called white blood corpuscle id). 



The human red blood cells are diminutive structures ; they 

 measure only 0.0088 to 0.0054 mm. Their smallness and their 

 innumerable quantity renders it possible that a small space — 

 a cubic millimetre of blood — may contain five millions of 

 them. 



Their form, as Fig. 10 

 showed, is spherical, the 

 periphery appears yellow, 

 the centre bright and 

 nearly colorless. When 

 the blood corpuscle rolls 

 over the microscopical 

 glass slide, the side view 

 presents the appearance 

 of c. Our cell, conse- 

 quently, represents a cir- 

 cular disc, with excavated 

 central portions of both 

 broad surfaces. 



Fig. 28. — Red blood corpuscles of man 

 with water ; b, in evaporating plasma ; 



a, treated 

 dried ; it, 



after coagulation ; e, rouleaux-like arrangement. 



The red blood corpuscle is, besides, a very changeable 



