66 PERMANENT TISSUES. 



isolated cells, for example, passing over into those with 

 blended walls ; and again, a tissue which usually consists of 

 isolated cells, occasionally exhibits in different situations coa- 

 lesced cells. Such difficulties, however, present themselves in 

 all classifications of natural objects. Nature is very unwilling 

 to accommodate herself to our schemes. The object of her aim 

 is quite opposed to that of our intellect. She accords and ac- 

 commodates all contrarieties by gentle transitions : the intellect 

 disjoins, and seeks everywhere for strongly-marked contrasts. 

 If, however, regard be had to the most important structure 

 only in each individual tissue, — for example, in the nervous 

 system, to the nervous fibres and not to the ganglion-globules, 

 in cellular tissue, to its fibres and not to the fat, and so 

 forth, — and further, if we regard only that which is the general 

 rule as to these structures, all tissues may then be readily 

 brought under these five classes. With the desire of making 

 this work as complete as possible, I have applied this arrange- 

 ment to all the tissues in the way which has appeared to be 

 most probably correct, according to the investigations I have 

 hitherto made. Those researches are, however, far from com- 

 plete, and continued observations may perhaps render it 

 necessary, at some future time, to assign a different position 

 to some of the tissues. This may serve as a preliminary 

 sketch : 



Class I. Isolated, independent cells. To this class the cells 

 in fluids pre-eminently belong ; Lymph- globules, Blood- 

 corpuscles, Mucus- and Pus -corpuscles, &c. 



Class II. Independent cells united into continuous tissues. 

 Such as the Horny tissues and the Crystalline lens. 



Class III. Cells, in which only the cell-walls have coalesced: 

 Cartilage, Bone, and the substantia propria (ivory) of the 

 Teeth. 



Class IV. Fibre-cells : Cellular (areolar), Fibrous, and 

 Elastic tissue. 



Class V. Cells, in which both the cell-walls and cell- 

 cavities have coalesced : Muscle, Nerve, Capillary 

 vessels. 



