CHAPTER I. 



Cells and Epithelial Membranes. 



SECT. I. The simple cell is the organ which above 

 all others is especially endowed with vital power, it 

 is the formative element, in fact, of all the simple 

 tissues, and is therefore, of necessity, our first object 

 of study. 



In every perfect cell we recognise the following 

 parts : (1) A containing membrane, transparent, struc- 

 tureless, and exceedingly thin and delicate the cell- 

 wall ^ within this envelope (2) a liquid substance, 

 generally transparent and granular, surrounding an- 

 other vesicle, which usually presents a more strongly 

 marked outline and thicker walls than those of the 

 cell, called the nucleus, or cyto blast ; and finally, (3) 

 in the midst of the granular contents of this latter, 

 we can detect, ordinarily, a granular body larger than 

 the rest, known as the nudeolus. (PI. I. fig. II. 1, 2, 

 3. PL II. fig. VI, VII. PI. XIII, fig. I). 



Whenever these constituent parts cannot be recog- 

 nised in a cell, it is to be inferred that it has already 

 undergone transformation from its original condition, 

 as we find to be the case, for example, in blood glo- 

 bules (PI. I. fig. I. 1), and fat cells (PL I. fig. V.) 



The contents of the cell, exclusive of its nucleus 

 and nucleolus, have been described as ordinarily 

 liquid, transparent, and finely granular. Sometimes, 

 however, these transparent granules are replaced, 



of 



