174 SCIENCE FROM AN EASY CHAIR 



microscopes, a structure like that of the vegetable " cell " 

 and its " nucleus " was discovered in some animal materials, 

 or " tissues," as they are termed for instance, in carti- 

 lage (Fig. 39). The word "tissue" is applied to each of 

 the various layers and masses, such as epiderm, fibrous 

 tissue, muscle, nerve, cartilage, bone, which can be dis- 

 tinguished in an animal body and separated from one 

 another, just as we may separate the "tissues" of a 

 man's clothes the leathern, woollen, silken, cotton, 



linen : the cords, laces, 

 threads, and pads or 

 stuffing. The full 

 meaning of this exist- 

 ence of "cells" or 

 " cellular " structure 

 in the tissue of plants 

 and animals only 

 gradually became evi- 

 dent. A very re- 

 FIG. 39. A piece of cartilage, showing the markable discoverer, 



cells which have formed it embedded in Professor Schwann, of 

 the (shaded) firm substance, and con- Liege (with whom 



when he was an old 

 man I spent an after- 

 noon a great many years ago), was the first to grasp the 

 great facts and to put forward what has been ever since 

 called " the cell theory " of animal and vegetable struc- 

 ture and life. 



Schwann, in 1836, showed that the important thing 

 about a " cell " is not the box or cell-wall so much as 

 the viscid contents and the nucleus. But the name 

 " cell " was (strangely enough) retained for the contents, 

 even when the box-like chamber was absent much as 

 we speak ol " a bottle of wine," meaning the contents of 

 the bottle, and not the glass vessel holding it. It was 



nected to one another by branching pro- 

 cesses of protoplasm. 



