INTRODUCTION. 9 



of form which it induces, and with ascertaining in what group of 

 chemical substances this or that part of a tissue should be classed. 

 Micro-chemistry must rather furnish us with the means of extract- 

 ing from the tissue to be examined one chemical constituent after 

 another, and of thus rendering them more accessible to further 

 chemical investigation. We believe that the following pages pre- 

 sent some striking illustrations of the advantages of this appli- 

 cation of micro-chemistry, which has first indicated the method of 

 investigating the chemical nature of the textures by the separation 

 of the less essential parts interwoven with them ; it will thus 

 throw some light on the constitution of parts like the brain, which 

 have hitherto defied all the eiforts of pure analysis. 



If we glance at the somewhat numerous micro- chemical reac- 

 tions which have been observed in the different tissues, we shall 

 find that they have rather excited our hopes than fulfilled our 

 expectations. The large number of reagents often scarcely differ- 

 ing in their actions, and their unsystematic accumulation, show 

 clearly enough that this branch of science has as yet been little 

 cultivated, and is but ill adapted to lead us to any explanatory 

 facts. But the cause of the unsatisfactory nature of the efforts 

 hitherto made to advance histo-chemistry by means of micro-che- 

 mical experiments, is to be referred less to the inefficiency of our 

 micro-chemical agents, than to the imperfect development of general 

 zoo-chemistry or the theory of the animal substrata. We cannot, 

 however, hope to make great or brilliant progress in the chemical 

 knowledgeof the tissues until chemists shall have succeeded in throw- 

 ing light upon the protein bodies, until better analytical methods 

 are discovered for the distinction and separation of these widely 

 differing, although in some respects analogous substances, or until 

 some more reliable methods can be adopted for the establishment 

 of less hypothetical formulae than those hitherto employed as, for 

 instance, in the case of albuminous substances. The protein 

 hypothesis has frequently served as the Trpwrov 'tyevSos for giving 

 scope to hazardous conjectures on the nature and formation of the 

 tissues, as well as on the entire metamorphosis of matter in the 

 animal body. We have, therefore, abstained as far as possible 

 from giving the artificial formulae and equations by which it has 

 been attempted to exhibit an ideal connexion between the compo- 

 sition of the different tissues and their origin and metamorphosis, 

 since it appears to us that science in its present undeveloped state 

 more especially demands caution in the indulgence of fanciful 

 hypotheses. A cautious reserve in this respect is more especially 



