Bauhaus-Universität Weimar

Handbook for the Physiological Laboratory. Text
Burdon-Sanderson, John Scott E. Klein Michael Foster T. Lauder Brunton
edgewise it appears spindle-shaped, because the thickness of 
the nucleus is greater than that of the cell. Besides these 
we find smaller polyhedric pavement cells, which consist of a 
nearly uniformly granular protoplasm, and possess one, or very 
rarely two, roundish, clear, and sharply-defined nuclei, with one 
or two large granules—i.e., nucleoli—within them. Finally, 
if we have scraped very energetically with the scalpel, we meet 
with cells corresponding to the deepest layers, which possess 
more of a cylindrical form, and contain an oblong nucleus. 
Similar results may be obtained if we macerate a portion of the 
mucous membrane in bichromate of potash solution. 
To study the epithelium of the cornea in the fresh condition 
we proceed in a somewhat similar way. A frog is held by an 
assistant, its nictitating membrane drawn down, and from the 
anterior corneal surface a thin layer is scraped with a lancet- 
shaped, or a cataract knife ; the fragment removed is then 
broken up and covered in aqueous humour, or in half per cent, 
solution of common salt. Here we find not only isolated cells, 
but connected masses of epithelium arranged in layers. By 
means of the fine adjustment the individual cells of these layers 
may be studied ; but we shall not at present occupy ourselves 
further either with the epithelium of the anterior corneal surface, 
or with the membrana Descemeti, since they will be fully described 
when we treat of the cornea. 
The epithelium of the skin (epidermis), and especially of the 
elements of the stratum corneum, may be readily brought under 
investigation as follows :—A small shred is raised from either 
the back, or palm of the hand, and covered in water; reagents 
which act upon horny structures, as, e.gdilute and concentrated 
acids and alkalies, may then be added. For the study of the 
cells of the Reta Malpighii, or portion of the epidermis which 
lies upon the corium, or true skin, the pointed condylomata so 
frequently met with, are peculiarly suitable. Cancroid tumours 
are equally to be recommended. We place these structures in a 
sherry-coloured solution of bichromate of potash, and let them 
macerate there for several days. At the end of this time we 
scrape off a small portion of the epithelium with a scalpel, 
transfer it to a drop of water or bichromate solution on a slide, 
break it up with a needle-handle, and apply the cover-glass as 
usual. In such preparations we meet with very striking forms 
of the so-called ridged cells, i.e., polyhedric cells w7hose surfaces 
are covered with ridges and intermediate furrows, and whose 
borders therefore, when seen in profile, appear as if serrated. 
Wherever two such surfaces are applied to each other, the ridges 
of the one fit into the furrows of the other, the line of adapta¬ 
tion being a zigzag one. The granular protoplasm of the indi-


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