FOURTH LECTURE. 



THE CONNECTIVE-SUBSTANCE GROUP. — CARTILAGE, GELA- 

 TINOUS TISSUE, RETICULAR CONNECTIVE TISSUE, FAT. 



CONNECTIVE TISSUE, fat tissue, cartilage, bone, dentine, are 

 well known constituents of the body. Their finer structure 

 proved extremely heterogeneous at the commencement 

 period of modern microscopy. It was in the year 1845 tna t: 

 Reichert recognized all these things as members of a natural 

 unity. Science is indebted to him for the exposition of a 

 " connective-substance group." Here Virchow accomplished 

 further progress in the domain of pathology ; and, indeed, 

 also committed errors. Much labor has subsequently been 

 bestowed upon this group ; we have made further progress, 

 but are still far enough removed from a conclusion. 



All these tissues mentioned — and to these are to be added, 

 as new acquisitions, gelatinous tissue and the reticular con- 

 nective substance — arise from the middle germinal layer (p. 

 26). They are originally similar, but then, pressing on to- 

 wards maturity, they assume quite variable forms. Connect- 

 ing intermediate forms, however, remain. No one can, for 

 example, draw a sharp boundary between gelatinous and 

 ordinary connective tissue, or between the latter and carti- 

 lage. We meet in places, therefore, with a continuous tran- 

 sition of one connective substance form into another. Truly 

 different tissues never do this. We meet, furthermore, in 

 the animal kingdom, very frequently a substitution of one 

 tissue of our group by another. That, for example, which 

 in one creature is connective tissue is in another gelatinous 

 tissue, or even bone. A temporary substitution also occurs. 

 The parts of our skeleton were, for the most part, formerly 

 cartilage. In morbid growths we meet with extraordinary 

 frequency with such substitutions of the one for the other. 



