CLASSIFICATION OF THE TISSUES. 23 



with the main portion by means of a thin, pedicle-like bridge. 

 The strangest appearances are hereby presented to the eye. 

 It is plain that only a membraneless cell body can present 

 such constrictions. 



The cells, these living corner-stones of our body, are other- 

 wise quite similar in the various vertebrate animals ; it is not 

 so, however, with the blood. The differences in most of the 

 mammalia are certainly slight. The form remains ; only the 

 diameters vary somewhat. A few ruminants, the camel, al- 

 paca, and llama, have oval cells (Fig. 29, 2). 



The blood corpuscles of birds (3), amphibia, and most 

 fishes (3), appear elliptic ; but in the middle of both broad 

 surfaces we meet with an elevation. The diameter changes 

 in an interesting manner. In birds, it is 0.0184 to 0.0150 mm.; 

 in the squamigerous amphibia, 0.0182 to 0.0150; in osseous 

 fishes <7j, 0.0182 to 0.01 14. Our cells reach prodigious dimen- 

 sions in the ray and shark, 0.0285 to 0.0226 mm.; then among 

 the batrachia, the frog (6) and the toad have blood corpuscles 

 of 0.0226; the triton (5), up to 0.0325 mm.; and the salamander 

 has still larger. The group of the pisciform amphibia have the 

 largest of all. In the proteus they measure 0.057 mm. The 

 cyclostomen, a low group of fishes, have, strangely, again, 

 spherical bi-concave discs measuring 0.0113 mm. (8). 



All these blood corpuscles behave, with reagents, similar 

 to those of man and the mammalia. But in them all, on the 

 contrary, there is a nucleus. Even in the dying cell it is 

 visible. Many reagents — for example, water, very dilute 

 acetic acid — let it show out from the now discolored cell as a 

 granular structure (Fig. 30, a, b). 



The second element of the blood, the 

 lymphoid cell, is much more homogeneous. 

 The form is, throughout, spherical ; the size 

 is, in man (Fig. 10, d ; Fig. 31, 1 to 4), rarely FlG . 30 ._Kio ? d 



„ „ n j_ __,__ , „„„ i-i cells of the fro^ with 



0.005, generally 0.0077 to 0.012 mm. I he granular nuclei, 

 most of our structures, according to this, 

 exceed the dimensions of the colored corpuscles. It is the 

 same in the mammalia. In the remaining classes of the 



