32 LECTURE I. 



genized membrane of nitrogenized contents differing 

 from it. 



It had indeed already long been known, that other 

 things besides existed in the interior of cells, and it was 

 one of the most fruitful of discoveries when Robert 

 Brown detected the nucleus in the vegetable cell. But 

 this body was considered to have a more important 

 share in the formation than in the maintenance of cells, 

 because in very many vegetable cells the nucleus be- 

 comes extremely indistinct, and in many altogether dis- 

 appears, whilst the form of the cell is preserved. 



These observations were then applied to the consider- 

 ation of animal tissues, the correspondence of which 

 with those of vegetables Schwann endeavoured to de- 

 monstrate. The interpretation, which we have just 

 mentioned as having been put upon the ordinary forms 

 of vegetable cells, served as the starting-point. In this, 

 however, as after-experience proved, an error was 

 committed. Vegetable cells cannot, viewed in their 

 entirety, be compared with all animal cells. In animal 

 cells, we find no such distinctions between nitrogenized 

 and non-nitrogenized layers ; in all the essential con- 

 stituents of the cells nitrogenized matters are met with. 

 But there are undoubtedly certain forms in the animal 

 body which immediately recall these forms of vegetable 

 cells, and among them there are none so characteristic 

 as the cells of cartilage, which is, in all its features, ex- 

 tremely different from the other tissues of the animal 

 body, and which, especially on account of its non-vascu- 

 larity, occupies quite a peculiar position. Cartilage in 

 every respect stands in the closest relation to vegetable 

 tissue. In a well-developed cartilage-cell we can dis- 

 tinguish a relatively thick external layer, within which, 

 upon very close inspection, a delicate membrane, con- 

 tents, and a nucleus are also to be found. Here, there- 



