58 HORNY TISSUE. 







These tissues differ also in the quantity of inorganic matter 

 which they contain, but this difference does not vary much 

 beyond 1^. 



On boiling these tissues with a solution of potash, they generally, 

 as we have already seen, become dissolved, with the exception of a 

 comparatively very small residue : a large quantity of ammonia is 

 developed, and the fluid contains much sulphide of potassium, the 

 presence of which may be detected immediately after the first 

 application of the alkaline fluid. When the alkaline solutions are 

 saturated with acetic, hydrochloric, or other acids, precipitates are 

 formed which, according to Mulder, differ in the character of their 

 composition. These deposits exhibit the property of adhering 

 together, and forming almost resin-like masses on being heated in 

 water. Mulder includes them amongst his protein-oxides. 



It will scarcely be necessary, after this notice of the reactions 

 exhibited by these tissues, to remark that our knowledge of their 

 chemical history is still too deficient, in a histological point of 

 view, to afford any satisfactory reply to the questions already pro- 

 pounded. For although Mulder,* in his most recent communica- 

 tions, has calculated formulae from his experiments, and has been 

 consequently led to regard all these tissues as combinations of 

 protein or protein-oxides with sulphamide, this hypothesis must 

 certainly be limited to one of the main constituents of the horny 

 tissue only, and cannot refer to the whole mass. Every horny 

 tissue contains at least three different kinds of substances : namely, 

 the substance of the cell-membranes, which is so difficult of solu- 

 tion in alkalies ; the cell-contents, including the nucleus, which 

 dissolve more readily in alkalies ; and the granular matters, con- 

 sisting by no means of fat solely, which remain after the complete 

 solution of some of these tissues, and are wholly insoluble in 

 alkalies. These three chemically-demonstrable matters can hardly 

 be regarded as isomeric or polymeric, and could not, even in 

 that case, be brought forward in support of the sulph amide hypo- 

 thesis. 



The principal portion of every horny tissue is formed, as we 

 have already observed, by the cell-membranes ; their contents and 

 the nucleus being so subordinate to these that the elementary 

 analysis of such a tissue must be regarded as giving an average 

 expression for the composition of these cell-membranes. They 

 do not behave, however, as if they consisted of a sulphamide 

 compound, for micro-chemical examination shows that the ammonia 

 * Untersuch. iibers. v. Volcker. H. 2, S. 272. 



