302 SOLID PARTS OF ANIMALS. 



creasing in length, being protruded from the roots, and seems at 

 first to be soft or nearly gelatinous. Every hair is a tube con- 

 taining a delicate organ, which supplies the hair with the requi- 

 site degree of moisture. In certain diseases, as the plica polo- 

 nica, this membrane swells so much that when the hair is cut, a 

 liquid, and even sometimes blood exudes. In their natural state, 

 the hairs are dry and insensible, and do not alter their appear- 

 ance by keeping. 



When hair is boiled in water, a portion is dissolved. This 

 portion gelatinizes on the water cooling, and possesses the cha- 

 racters of gelatin. Hair thus treated becomes much more brit- 

 tle than before. Indeed, if the process be continued long enough, 

 the hair crumbles to pieces between the fingers. The portion in- 

 soluble in water possesses the properties of coagulated albumen. 



Mr Hatchett has concluded from his experiments, that the 

 hair which loses its curl in moist weather, and which is the softest 

 and most flexible, is that which yields its gelatin most easily ; 

 whereas strong and elastic hair yields it with the greatest diffi- 

 culty, and in the smallest proportion. This conclusion has been 

 confirmed by a very considerable hair-merchant in London, who 

 assured him that the first kind of hair was much more injured by 

 boiling than the second. 



Though hair be insoluble in boiling water, Vauquelin* obtain- 

 ed a solution by raising the temperature of the liquid in a Papin's 

 digester. If the heat thus produced was too great, the hair was 

 decomposed, and ammonia, carbonic acid, and an empyreumatic 

 oil formed. Sulphuretted hydrogen is always evolved, and its 

 quantity increases with the heat. When hair is thus dissolved in 

 water heated above the boiling point, the solution contains a kind 

 of bituminous oil, which is deposited very slowly. This oil was 

 black when the hair dissolved was black, but yellowish-red when 

 red hair was employed. 



When the solution is filtered to get rid of this oil, the liquid 

 which passes through is nearly colourless. Copious precipitates 

 are formed in it by the infusion of nut-galls and chlorine. Silver 

 is blackened by it, and acetate of lead precipitated brown. Acids 

 render it turbid, but the precipitate is redissolved by adding 

 these liquids in excess. Though very much concentrated by 

 evaporation, it does not concrete into a jelly. 



* Nicholson's Journal, xv. 141. 



