4 INTRODUCTION. 



are to be examined on all sides and not only in fully-formed 

 structures, but in all tlie earlier periods from their first develop- 

 ment. When the morphological elements have been perfectly 

 made out, the next object is to discover the laws according to 

 which they arise, wherein one must not fail to have regard 

 also to their relations of composition and function. In dis- 

 covering these laws, here as in the experimental sciences 

 generally, continual observation separates more and more, 

 among the collective mass of scattered facts and observations, 

 the occasional from the constant, the accidental from the 

 essential, till at last a series of more and more general ex- 

 pressions of the facts arises, — from which, in the end, mathe- 

 matical expressions or formula proceed, and thus the laws are 

 enunciated. 



If we inquire how far Histology has satisfied these require- 

 ments, and what are its prospects in the immediate future, the 

 answer must be a modest one, Not only does it not possess a 

 single law, but the materials at hand from which such should 

 be deduced, are as yet relatively so scanty, that not even 

 any considerable number of general propositions appear well 

 founded. Not to speak of a complete knowledge of the 

 minuter structure of animals in general, we are not acquainted 

 with the structure of a single creature throughout, not even of 

 man, although he has been so frequently the object of investi- 

 gation, — and therefore it has hitherto been impossible to bring 

 the science essentially any nearer its goal. It would, however, 

 be unjust to overlook and depreciate what we do possess ; and 

 it may at any rate be said, that we have acquired a rich store 

 of facts and a few more trustworthy general propositions. To 

 indicate only the more important of the former, it may be 

 mentioned, that we have a very sufficient acquaintance with 

 the perfect elementary parts of the higher animals and that 

 we also understand their development, Avith the exception of 

 the elastic tissue, and of the elements of the teeth and bones. 

 The mode in which these are united into organs has been less 

 examined, yet on this head also, much has been added of late, 

 especially in man, whose individual organs with the exception 

 of the nervous system, the higher organs of sense and a few 

 glands (the liver, blood-vascular glands), have been almost 

 exhaustively investigated. If the like progress continue to 



