TISSUES OF THE BODY. 167 



In the first place, comparative histology teaches that the different forms 

 which belong to this group of connective tissues replace each other 

 frequently enough. What is in one animal, for instance, ordinary con- 

 nective tissue appears in another 'in the form of reticular substance, 

 cartilage, or bone. The cartilage of some organs in one being is replaced 

 in the same parts of another by bone, or bony tissue by dentine, and 

 so on. 



But in one and the same organism also typical development brings 

 with it a substitution of one member of the connective-substance group 

 for another. There, for instance, where in the embryonic state gelatinous 

 tissue existed, the latter is found transformed into connective tissue or 

 fat at a later epoch; cartilage with its derivatives takes on the form of 

 bony substance. 



Finally, we encounter every kind of this substitution in the richest 

 abundance in pathological research, brought about by formative activity 

 of a system modified by disease. Almost every member of the group of 

 connective tissues may be replaced by very nearly any other, firstly by 

 immediate metamorphosis, then again more particularly by reconstruction 

 from the offspring of the original tissue. 



Now, while we thus have sufficient examples of relationship on anatomi- 

 cal territory, all the tissues of this group are also found to correspond in 

 another respect, namely, from a physiological point of view. Their signifi- 

 cance in the actions of the healthy body is of a more subordinate kind, 

 although they make up an enormous proportion of it. They represent, as 

 is usually said, tissues of lower vital dignity, certain connecting, enclosing, 

 or supporting matters in our system, or a kind of widely distributed 

 framework, in whose interspaces other tissues, as, for instance, muscles, 

 nerves, vessels, and gland-cells, lie imbedded. The name, therefore, " con- 

 nective-substance," formed after that of " connective-tissue " proposed by 

 Miiller, appears in many respects a suitable one. The term " sustenta- 

 cular tissue " applied to it by KoUiker might also be recommended. 



However, though connective-substance takes but little part in the phy- 

 siological occurrences of the mature and healthy body, as we have just 

 said, it loses this character of quiescence and indifference in the 

 numerous transformations and luxuriant growths of the diseased body, 

 and becomes on the contrary the most active tissue of the whole system. 

 We are indebted to Virchow for having brought out, by an extensive 

 series of observations, that it is principally from the tissues of the con- 

 nective-substance group that most of the pathological new formations 

 take their rise, " so that the connective-tissue with its equivalents may 

 be regarded as the common germ-bed of the body." 



REMARKS. Science has to thank Reichert for having in the year 1845 placed our 

 views as regards connective-tissue on a firm basis. 



102. 



Now, although it is comparatively easy to sketch the first outlines of 

 the connective : substance group, definition in individual cases, and the 

 arrangement of the various forms of tissue by means of the history of 

 their development, is attended at present with the greatest difficulty. 



Indeed, the requirements of histology on these points can be only but 

 very imperfectly satisfied in the present state of science. In the first 

 place, there still exist great gaps, and then the earlier and more extensive 

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