SECTION III 



THE TISSUES 



FROM the protoplasm of the cells the various tissues of the 

 body bone, cartilage, muscle, etc. are formed. The structure 

 of these must be studied practically ; all that will be attempted 

 here is to indicate how they are formed from the primitive 



cell. 



The human body is originally a single cell, and from this, 

 by division, a mass of simple cells is produced. In the embryo, 

 these cells get arranged in three layers an outer, a middle, 

 and an inner the epiblast, mesoblast, and hypoblast (fig. 176, 



p. 445). 



(A) THE VEGETATIVE TISSUES 



The Vegetative Tissues are those which support, bind to- 

 gether, protect, and nourish the body. They may be divided 

 into the Epithelial Tissues, formed from the epiblast or hypo- 

 blast, and consisting of cells placed upon surfaces, and the 

 Connective Tissues developed from the mesoblast, and consisting 

 chiefly of formed material between cells. 



I. EPITHELIUM 

 1. Squamous Epithelium 



(a) Simple Squamous Epithelium. This is seen lining the 

 air vesicles of the lungs. It consists of a single layer of flat, 

 scale-like cells, each with a central nucleus. The outlines of 

 these cells are made manifest by staining with nitrate of silver, 

 which blackens the cement substance between the cells. 



(6) Stratified Squamous Epithelium (fig. 4). The skin and 

 the lining membrane of the mouth and gullet are covered by 

 several layers of cells. The deeper cells divide, and as the 

 young ones get pushed upwards towards the surface, and away 

 from the nourishing fluids of the body, their nutrition is 

 interfered with, and the protoplasm undergoes a change into a 



