CHAP. XIV.] LYMPHATICS OF THE SKIN. 421 



from coagulated albumen or fibrine by its being readily soluble 

 in caustic fixed alkalies, but not in caustic ammonia. The ashes of 

 hair amount, according to Vauquelin, to one and a half per cent, of 

 its weight ; and contain oxide of iron, a trace of oxide of manganese, 

 of sulphate, phosphate, and carbonate of lime, and of silica. Black 

 hair contains most iron, and light hair least * 



Hairs, when dry and warm, are easily rendered electrical. They 

 readily attract moisture from the atmosphere, and no doubt from 

 the body also, yielding it again by evaporation, if the air be dry. 

 When moist, they elongate considerably ; a property which Saus- 

 sure took advantage of in the construction of his hygrometer, in 

 which a human hair, by its elongation and shortening in moisture 

 and dryness, is made to turn a delicate index. 



The shape of the hairs in different situations offers some variety. 

 In general, they taper towards their free end. Those of the head 

 are often not cylindrical, but compressed on one or both sides, so 

 that their transverse section is reniform or oval. The eye-brows 

 and eye-lashes taper towards both extremities. Hairs also vary in 

 being lank or woolly, permanent or deciduous. The frizzled hair 

 of the negro is one of his most remarkable characteristics, but has all 

 the essential structural characters of the hairs of the other races. 



The diseased condition called plica Polonica is a matting together 

 of the hairs, from the effusion of a glutinous matter, probably 

 from the cutaneous glands. It is said that hairs so affected bleed, 

 if cut close to the skin. This, if true, may result from a morbid 

 elongation of the vascular papillae at their roots. In the whiskers 

 of large animals these papillae are so long, that they are cut and 

 bleed if the whiskers are shaved off. 



In some regions of the skin it appears certain that a lymphatic 

 network exists immediately under the surface of the cutis, probably 

 under its basement membrane. Mercury injected into this network 

 through a puncture in the cuticle passes readily into the neighbour- 

 ing lymphatic trunks, and removal of the cuticle does not injure its 

 meshes. These circumstances may be observed in the penis, scro- 

 tum, and nipple : but it is probable that the network sometimes 

 exhibited by this procedure in other parts of the skin, is a fallacious 

 appearance due to the mercury having insinuated itself between 

 the cutis and cuticle, in the furrows at the base of the papillary 

 structure ; for it does not find its way into the lymphatic trunks, 

 and is deranged by a complete separation of the cuticle.t 



* Baly's Miiller, p. 424-5, quoted from Berzelius. 



t Cycl. of Anat. and Ph ys. ; art. Lacteal and Lymphatic System : by Mr. Luiio. 



