GENERAL OBSERVATIONS 



59 



Horn appears to be identical with epidermis, hair, wool, 

 feathers, and whalebone, in yielding ' keratin,' a substance 

 intermediate between albumin and gelatine, and containing 

 from 60 to 80 per cent, of sulphur. 



That horn is combustible everyone who has watched 

 the fitting of a hot shoe knows. That it is a bad con- 



Fig. 31. — Perpendicular Section of Horn of Wall. 



ductor of heat, the absence of bad after-effects on the foot 

 testifies. 



In a previous page we have described the manner of 

 growth of the horn tubules, and noted the direction they 

 took in the wall ; also we have noticed the existence be- 

 tween them of an intertubular horn or cement. 



Those who wish to give this subject further study will 

 find an excellent series of articles by Fleming in the 

 Veterinarian for 1871. We shall content ourselves here 

 with introducing one or two diagrams and photo-micro- 

 graphs, and dealing with the histology very briefly. 



Under the microscope the longitudinal striation of the 

 wall is found to be due to the direction taken by the horn 

 tubules. 



