PHYSIOLOGY OP TOUCH. 

 Fig. 50. 



133 



Diagram of the Structure of an Involuted Mucous Membrane, showing the continuation of its 

 elements in the follicles and villi. 



F, P. Two follicles, b. Basement membrane, c. Submucous tissue, e. Epithelium, v. Vascular 

 layer, n. Nerve, v. Villus, covered with epithelium, v'. Villus, whose epithelium has been shed. 



epithelial cells lying upon it ; the base being free. Each cell, nearly 

 midway between the base and apex, encloses a flat nucleus with nucleoli. 



Fig. 51. 



Cylinders of Intestinal Epithelium. (After Henle.) 



A. From the cardiac region of the human stomach. B. From jejunum, c. Cylinders seen when 

 looking on their free extremities. D. Ditto, as seen in a transverse section of a villus. 



Epithelium is sometimes furnished with cilia, or is said to be ciliated. 

 The nature and uses of these cilia, as well as the different varieties of 

 mucous membrane, will be described hereafter. 



2. PHYSIOLOGY OF TAGT AND TOUCH. 



In describing the physiology of the sense of touch, it will be conve- 

 nient to revert to the distinction already made between the sense when 

 passively and actively exerted ; or between tact, and touch. The mode, 



