TISSUES OF THE BODY. 



153 



with the description just given, while the more superficial scale-like forma- 

 tions, at one time nucleated, at another not so, give the reactions of keratin. 



This represents, naturally, a mixture of substances; it forms the nucleus, 

 contents, envelope of these elements, and the scanty intercellular matter; 

 the residue after treatment with water, alcohol, and ether. 



This mixture is then insoluble in cold as well as boiling water, and (if 

 not contaminated with other elements of connective tissue) yields no glutin 

 on boiling ; nor is it acted on by acetic acid. Even to sulphuric acid, in 

 which it becomes puffy, it offers a certain amount of resistance. With 

 hydrochloric and sulphuric acid it gives the reactions of the protein sub- 

 stances. 



Its conduct toward alkalies is, however, of the greatest importance: 

 with them keratin enters into combination, at the same time that it puffs 

 out or becomes gelatinous, and is subsequently dissolved on the addition 

 of water. If to such a solution of keratin acetic acid be added, certain 

 products of the decomposition of the albuminoid group are precipitated. 



The swelling up of this tissue before solution, as it occurs both in cold 

 and heat, has much interest for the anatomist (fig. 150). In order to 

 produce this appearance, we treat the epidermis either with a very strong 

 caustic solution, and then with water, or we employ from the commence- 

 ment more dilute reagents. On this the older cells become puffed out 

 into spheroids (1 b-f, 2 b, c), lose their flattened figure, and again assume, 

 in the most striking manner, their original cellular character, the contents 

 beginning to dissolve in the imbibed fluid, and the envelope to become 

 sharply defined. At the same time, also, the stratification of the epithelial 

 beds becomes distinctly visible, so that in this respect likewise alkalies 

 may be of the greatest service to microscopists. Later on the nucleus is 

 attacked (1 b-d), and 

 then the intercellular 

 matter. Finally the 

 envelope is dissolved, 

 but only if the cell be 

 not one of those which 

 have been completely 

 converted into horny 

 matter. Very old squam- 

 ous elements possess, on 

 the other hand, a mem- 

 brane which reminds us 

 in its great capacity for 

 resistance to alkalies, of 

 the substance of the elas- 

 tic tissues. The addi- 

 tion of acetic acid pro- 

 duces in the cell which 

 has gelatinised in the 

 manner described, a 

 precipitate of decom- 

 posed protein substances 

 already mentioned (1 #, 

 2 d\ " 



After what has just 

 been remarked, there can be hardly any doubt that keratin partakes of 



Fig. 150. 1. Epithelial cells. At cr, an unchanged flat cell from 

 the mouth ; from 6 to /, the same kinds of cells after treat- 

 ment with caustic soda, some containing nuclei (6 c d) and some 

 not; g, on the addition of acetic acid, after treatment with caustic 

 soda. 2. Epidermal cells, a, unchanged; b, commencing action 

 of the soda; at c, after prolonged action of the same; d, on the 

 addition of acetic acid. 



