274 THE CELL-THEORY 



in reality exactly the same mode of metamorphosis of the same 

 elements as in the preceding instance. Connective tissue, therefore, 

 we may say, consists in its earliest state of a homogeneous periplast 

 inclosing endoplasts. The endoplasts may elongate to some extent, 

 but eventually become lost, and cease, more or less completely, to be 

 distinguishable elements of the tissue. The periplast may undergo 

 three distinct varieties of chemical differentiation, e.g., into the 

 gelatinous " intercellular substance," the collagenous " cell-wall," and 

 the elastic " cell-wall ; " and two varieties of morphological differentia- 

 tion, vacuolation, and fibrillation — and the mode in which these changes 

 take place gives rise to the notion that the perfect tissue is composed 

 of elements chemically and mechanically distinct. 



The proper understanding of the nature and mode of development 

 of the component parts of connective tissue is, we believe, of the first 

 importance in comprehending the other tissues. If we clearly bear in 

 mind, in the first place, that the periplast is capable of undergoing 

 modifications quite independently of the endoplasts ; and, secondly, 

 that in consequence of their modification, elements may become 

 optically, mechanically, or chemically separable from a perfect tissue 

 which were not discoverable in its young form, and never had any 

 separate existence ; many of the great difficulties and perplexities of 

 the cell-theory will disappear. Thus, for instance, with regard to the 

 structure of bone, there can be no doubt that the " nuclei " of the 

 corpuscles are endoplasts, and that the calcified matrix is the periplast. 

 This calcified matrix has, however, in adult bone, very often a very 

 regular structure, being composed of definite particles. To account 

 for these, Messrs. Tomes and De Morgan, in their valuable essay on 

 ossification, which has just appear-ed,^ suppose that certain " osteal 

 cells " exist and become ossified. We have no intention here of 

 entering upon the question of the existence of these " osteal cells " as 

 a matter of fact, but we may remark that they are by no means 

 necessary, as the appearance might arise from a differentiation of the 

 periplast into definite particles, corresponding with that which gives 

 to connective tissue its definite and fibrillated aspect. So with regard 

 to the vexed question whether the lacunce have separate parietes or 

 not, how readily comprehensible the opposite results at which different 

 observers have arrived become, if we consider that their demonstrability 

 or otherwise results simply from the nature and amount of the chemical 

 difference which has been established in the periplast in the immediate 

 neighbourhood of the endoplast with regard to that in the rest of the 

 periplast. In fig. 3 substitute calcific for collagenous metamorphosis, 



1 Phil. Trans., 1853. 



