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- 
commodatesall 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 ganghon-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 apphed 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. 
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