LAW OF CONTINUOUS DEVELOPMENT. 55 



are still a few spots in the body where absolute demon- 

 stration has not yet been afforded, the principle is 

 nevertheless established, that in the whole series of 

 living things, whether they be entire plants or animal 

 organisms, or essential constituents of the same, an 

 eternal law of continuous development prevails. There is 

 no discontinuity of development of such a kind that a 

 new generation can of itself give rise to a new series of 

 developmental forms. No developed tissues can be J 

 traced back either to any large or small simple element, t 

 unless it be unto a cell. In what manner this continuous 

 proliferation of cells (Zellenwucherung), for so we may 

 designate the process, is carried on, we will consider 

 hereafter ; to-day, my especial object only was to deter 

 you from assuming as the groundwork of any views you 

 might entertain with regard to the composition of the 

 tissues, these theories of simple fibres or simple globules 

 (elementary fibres or elementary globules). 



If it be wished to classify the normal tissues, a very 

 simple point of view, founded upon marked characteris- 

 tics, offers itself, upon which their division into three 

 categories may be based. 



We either have tissues which consist exclusively of 

 cells, where cell lies close to cell in fact, cellular tissue 

 in the modern sense of the word or we find tissues, in 

 which one cell is regularly separated from the other by a 

 certain amount of intermediate matter (intercellular 

 substance), and, therefore, a kind of uniting medium 

 exists, which, while it visibly connects the individual 

 elements, yet holds them separate. To this class belong 

 the tissues which are now-a-days generally comprehended 

 under the name of connective tissues (Gewebe der Bin- 

 desubstanz), and of which what was formerly universally 

 called cellular tissue constitutes the chief portion. 

 Finally, there is a third group of tissues, in which tho 



