18 GENERAL CONSIDERATIONS. 



then the whole cell seems to flow to and into its branch. (5) 

 Motion in response to various physical and chemical stimuli, 

 (c) The power of taking food, absorbing portions and rejecting 

 the rest, (c/) Reproduction of its kind. This is accomplished by 

 splitting of the cell into two, each with its own nucleus and life- 

 history, (e) Death, in which the constituent elements undergo 

 chemical changes. All cells follow more or less closely this cycle 

 of changes by which we diiferentiate living matter from unorgan- 

 ized substances. 



Name some of the kinds of cells found in man. 



Epithelial, connective-tissue, blood-, and nerve-cells. 



What is epithelium? 



The name " epithelium " is given to the cells which cover the skin, 

 mucous and serous membranes of the body, and also enter into the 

 formation of the glands. Its varieties are (1) Simple, a layer 

 of flat (squamous), cubical, (spheroidal), or cylindrical (columnar) 

 cells, as in the serous and mucous surfaces ; (2) stratified, when it 

 occurs in layers, as in the skin ; (3) transitional, where it has the 

 characteristics of both in situations where the other two forms 

 approach one another, as in the ureters. (4) In the glands are 

 found functional cells, which partake of the character of the epi- 

 thelium of the surface. They are arranged in groups about the 

 ducts. Such cells are often known as secreting or glandular epi- 

 thelial cells. 



What is ciliated epithelium? 



The simple epithelium possesses hair-like processes in certain 

 locations, and this is known as ciliated epithelium. The hairs are 

 endowed with motion, and wave in such manner as to throw for- 

 ward small particles which fall upon them. 



Name the chief uses of epithelium. 



Protection, as skin, serous surfaces ; motion, ciliated epithelium 

 of air-passages and Fallopian tubes ; secretion, in glands e. g. 

 gastric juice ; sensation, in the cones of the retina, olfactory cells 

 of nose, etc. 



What is endothelium ? 



It is a simple form of squamous or scale-like, flat epithelial cells 

 which line the serous membranes and the blood-vessels. The cells 



