1034 



VERTEBRATED ANIMALS 



substance of hairs, contains cells that have been so little altered as 

 to be easily recognised ; and the outer or cortical portion also may 

 be shown to have a like structure by macerating it in a solution of 

 potass and then in water. Sections of any of the horny tissues are 

 best mounted in Canada balsam. 



Blood. Carrying our microscopic survey, now, to the elementary 

 parts of which those softer tissues are made up that are subservient 

 to the active life of the body rather than to its merely mechanical 

 requirements, we shall in the first place notice the isolated floating 



cells contained in the blood, 

 which are known as blood-cor- 

 puscles. These are of two 

 kinds: the -red' and the 

 ' white ' or colourless.' The 

 red present, in every instance, 

 the form of a flattened disc, 

 which is circular in man and 

 most mammalia (fig. 767), but 

 is oval in birds, reptiles (tig. 

 FIG. 766. Red corpuscles of frog's blood: 766), and fishes, as also ill a 

 aa, their flattened face; b, particle turned f ew mamma ] s ( a ll belonging to 

 nearly edgeways ; c. colourless corpuscle ; , i "u \ T 



d, red corpuscles altered by diluted acetic the camel tribe). hi the one 

 acid. form as in the other, these 



corpuscles seem to be flattened 

 cells, the walls of which, how- 

 ever, are not distinctly dif- 

 ferentiated from the ground 

 substance they contain, as 

 appears from the changes of 

 form which they spontaneously 

 undergo when kept by means 

 of a 'warm stage" at a tem- 

 perature of about 100F., and 

 FIG. 767Red corpuscles of human blood, fr t j ff t f pressm . e in 

 represented at , as they are seen when 



rather within the focus of the microscope ; breaking them up. Lhe red 

 and at b, as they appear when precisely in corpuscles in the blood of 



oviparous Vertebral a are dis- 

 tinguished by the presence of a 



central spot or nucleus; this is most distinctly brought into view 

 by treating the blood-discs with acetic acid, which causes the nucleus 

 to shrink and become more opaque, whilst rendering the remaining 

 portion extremely transparent (fig. 766. </). lly examining un- 

 altered red corpuscles of the frog or neut under a sutliciently high 

 magnifying pouer the nucleus is seen to be tra\er>ed bv a network 

 "I filaments, which extends from it throughout the ground sub- 

 stance of the corpuscle, constituting an int racellular reticulation. 

 The red corpuscles of the blood of mammals, however, possess no 

 distinguishable nucleus, the dark spot which is seen in their centre 

 (lig. 767, A) being merely an effect of refraction, consequent upon 

 the double coiicaxe form of the disc. When these corpuscles are 

 treated with water, so that their form becomes first flat and then 



