INTRODUCTION. 3 



import of the nucleus, the development of the higher tissues, 

 their chemical relations, &c, has received a further development; 

 but all this has not amounted to a step so greatly in advance 

 as to constitute a new epoch. If, without pretensions to 

 prescience, it be permitted to speak of the future, this con- 

 dition of histology will last as long as no essential advance is 

 made towards penetrating more deeply into organic structure, 

 and becoming acquainted with those elements of which that 

 which we at present hold to be simple, is composed. If it be 

 possible that the molecules which constitute cell-membranes, 

 muscular fibrils, axile fibre of nerves, &c., should be discovered, 

 and the laws of their apposition, and of the alterations which 

 they undergo in the course of the origin, the growth, and the 

 activity of the present so-called elementary parts, should be 

 made out, then a new era will commence for Histology, and 

 the discoverer of the law of cell genesis, or of a molecular 

 theory, will be as much or more celebrated than the originator 

 of the doctrine of the composition of all animal tissues out 

 of cells. 



§ 2. 



In characterising the present position of Histology and of its 

 objects, we must by no means forget that, properly speaking, it 

 considers only one of the three aspects which the elementary 

 parts present to observation, namely, their form. Microscopical 

 anatomy is concerned with the understanding of the micro- 

 scopic forms, and with the laws of their structure and deve- 

 lopment, not with any general doctrine of the elementary 

 parts. Composition and function are only involved, so far 

 as they relate to the origin of forms and to their variety. 

 Whatever else respecting the activity of the perfect elements 

 and their chemical relations is to be found in Histology, is 

 there either on practical grounds in order to give some useful 

 application of the morphological conditions, or to complete 

 them ; or from its intimate alliance with the subject, it is 

 added only because physiology proper does not afford a due 

 place for the functions of the elementary parts. 



If Histology is to attain the rank of a science, its first need 

 is to have as broad and certain an objective basis as possible. To 

 this end, the minuter structural characters of animal organisms 



