260 THE TISSUES. 



is great, though so extensible. A hair of the head will support at 

 least six ounces without breaking. 



The hairs readily imbibe water, and as readily give it out again ; 

 hence they are sometimes dry and brittle, and sometimes moist and 

 soft, according fco the amount of moisture the skin or the atmo- 

 sphere contains. They are also longer or shorter, in proportion as 

 they contain more or less moisture; and hence their use in hy- 

 grometry. 



The hairs become slowly colored during their development; being 

 quite colorless in the embryo, and paler in youth generally than in 

 middle age. In the adult, the palest are the downy hairs which 

 have remained, as it were, in the foetal condition ; while the longer 

 ones, are always darker, and the darkest of all are those of the 

 head, beard, and pubes. 



The durability of the hair results from its indestructibility by 

 external agents, before alluded to. False hair may be continually 

 worn for many years. 



Distribution and Size of the Hairs. 



The hairs are distributed over every part of the surface of the 

 human body, except the palm of the hand and the sole of the foot, 

 the dorsum of the last joint of the fingers and toes, the inner sur- 

 face of the prepuce, the glans penis, the upper eyelids, and the lips. 

 They present differences in size and number in different regions ; 

 and also according to age, sex, race, and individual peculiarities. 



In size, three varieties maybe mentioned (Kb'lliker): 1. Long, 

 soft hairs, 1 to 3 feet and more in length, and g ^ to 2 J^ of an inch 

 in thickness ; 2. Short, stiff, thick hairs, J to J of an inch in length, 

 and ? ^o to T 4(7 of an inch thick; 3. Short and very fine hairs or 

 down (lanugo), T J 2 to ^ of an inch long, and ^Vir to ijzov thick. 

 The first includes the hairs of the head, beard, &c. ; the second, those 

 of the nostrils (vibrissas), the eyelashes (cilia), and those in the ex- 

 ternal auditory passage; the last includes the hairs on the face gene- 

 rally, on the trunk and extremities, on the caruncula lachrymalis, 

 and those (often absent) of the labia minora. (Henle.) Other things 

 being equal, black hairs are the coarsest, and blonde the finest. 



On the heads of females, the length of the hairs has sometimes 

 equalled that of the whole body, and the coarsest hairs are also 

 found on women. ( Wilson.) Beards also not seldom reach down to 

 the waist. 



The hairs are not true cylinders, as usually supposed, but present 



