GENERAL OBSERVATIONS 59 
| Wall. | Sole, | Frog 
Water ... lag ws a aid | 16:12 36:0 | 42:0 
Fatty matter ... stb , 0°95 0°25 0°50 
Matters soluble in water | 1°04 1°50 1:50 
Insoluble salts | 0°26 0°25 0:22 
Animal matter | 81°63 | 620 55°78 
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- 
Fic. 31.—Psrpenpicunar 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 
between 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. 
