INTRODUCTION. 3 



chemical analysis to accuracy, and which was itself in part based 

 on the attempt to establish a more intimate ideal connexion 

 between the results of the elementary analyses and the hypothetical 

 formula of the yet more hypothetical protein. 



Mulder himself was by no means unconscious of the imperfec- 

 tions of this method, and endeavoured in union with Donders to 

 approach this somewhat inaccessible department of science in a 

 totally opposite direction. The tissues to be examined were 

 exposed to the action of various chemical reagents^ and the changes 

 which their texture underwent were observed under the micro- 

 scope, with the view of deducing from them conclusions regarding 

 the differences in chemical constitution. This course was, how- 

 ever, first adopted by J. Miiller, who was led by it to several 

 results of much value in relation to physiology and general 

 anatomy. Several observers followed with more or less success 

 the path which he had thus marked out ; but their investigations 

 (unfortunately for us) had reference more to the histological than 

 to the chemical side of the inquiry. Histology has already derived the 

 most important aid from this method, since the reagents which we 

 apply to microscopical preparations are no longer limited to dilute 

 acetic acid, tincture of iodine, or, at most, perhaps a little ammonia. 

 It was by means of microscopico-chemical analysis that the struc- 

 ture of the different horny tissues was first clearly exhibited ; who 

 could formerly have established with such precision that nails, cows' 

 horn, and whalebone are composed of aggregations of individual 

 cells, from the most careful tracing of their developmental history ? 

 Would the axis-cylinder of the nerve-fibres have remained so long 

 unperceived, or at all events a subject of doubt, if at an earlier 

 period we had been more familiar with micro-chemical investiga- 

 tions ? Chemical appliances have often afforded most important 

 service to histology, even when not promoting our knowledge of the 

 chemical constituents of the tissues. We shall, therefore, be war- 

 ranted in assuming that the progress of histo-chemical inquiry will 

 be satisfactory, when micro-chemical investigation is directed and 

 regulated by the results of micro-chemical analyses; the micro- 

 chemical relations of a tissue serve to indicate the course that 

 must be pursued in order to lead to a successful investigation of the 

 chemical constituents of the tissue, and of its composition. 



These are, as we conceive, the points of view from which, in 

 the existing state of science, histo-chemistry ought to be inves- 

 tigated ; and in accordance with these ideas, we have attempted to 

 give a sketch of the mode in which it should be treated. 



B 2 



