IO4 THE TISSUES. 



Plasma cells (Unna) vary in size and shape according to the 

 space which they occupy. They may be round, oval, or /spindle- 

 shaped, and measure from 6 M to 10 /A The nucleus is round or 

 oval. They are characterized by the fact that their protoplasm 

 stains intensely in basic aniline dyes, often of a color differing from 



that of the solution used. Accord- 

 ing to some observers, the plasma 

 cells are thought to be developed 

 / from the connective-tissue cells, 



v, ^^bn while others regard tnem as de- 



, rived from the white blood-cells 



/^Tl^'A (lymphocytes). They are found u: 



Nucleus. t-'-i -I -I " \J^fJj 



'--\ / %. various mucous membranes and m. 



lymphoid tissues generally. 



Mast-cells (Ehrlich) are rela- 

 tively large cells of round, oval, or 

 irregular shape, the protoplasm of 

 which contains relatively large 

 granules which stain chiefly in 

 basic aniline dyes, which granules 

 Fig. 69. Leucocyte of a frog with are often found in such numbers 



pseudopodia. The cell has included a that they COVCr Up the nucleus, 



bacterium which is in process of diges- , o-^nnlps arf > Drained bv a 

 tion. (After Metschnikoff, from O. 



Hertwig, 93, II.) number of basic aniline dyes, often 



of a color differing from that of 



the stain used. They are found generally in mucous membranes, 

 generally near the vessels, in the skin, in involuntary muscle, and 

 in the bone-marrow. 



Pigment cells are branched connective-tissue cells, in the proto- 

 plasm of which are found brown or nearly black granules. In man 

 they occur in the choroid and iris and in the dermis. In the lower 

 animals they have, however, a much wider distribution, and in the 

 frog and other amphibia they are very large and irregular. These 

 cells have the power of withdrawing their processes and, to a limited 

 degree, of changing their location (dermis). 



The wandering or migratory cells are described in this connec- 

 tion not because they form one of the structural elements of areolar 

 connective tissue, but because they are always associated with it. 

 They are lymph- or white blood-cells, which have left the lymph- or 

 blood-vessels and have migrated into the lymph canalicular system. 

 They possess ameboid movement, and wander from place to place, 

 and are the phagocytes of Metschnikoff. They seem to be intrusted 

 with the removal of substances either superfluous or detrimental to 

 the body (as bacteria). These are either digested or rendered harm- 

 less. The wandering cells even transport substances thus taken up 

 to some other region of the body, where they are deposited. 



In the peritoneum and other serous membranes the network 

 formed by the fibrous tissue lies in one plane, and does not branch 



