62 DISEASES OF THE HORSE’S FOOT 
horn tubules in the frog. The peculiar, indiarubber-like 
toughness of this organ is well known. Histological 
examination gives a reason for this. 
The horn tubules of the frog are sinuous in their course. 
This is accounted for by the fact that in the horn of the. 
frog there is a large amount of intertubular material, this 
having the effect of frequently turning the horn tubules 
from the straight. In addition to this, the intertubular 
material has a peculiar arrangement of the cells composing 
it. These are laid down in alternating strie (1) of cells 
with their long axes longitudinal, and (2) of cells with their 
long axes horizontal. This is seen in Fig. 34, between the 
long papille of the corium, where the lines of longitudinally 
arranged cells in horizontal section stand out darker than 
the adjoining strata in which their arrangement is hori- 
zontal. The tortuous direction of the horn tubules, and — 
the almost interlocking nature of the alternating strata 
of the intertubular material, together combine to give the 
frog its characteristic toughness and resiliency. 
C. EXPANSION AND CONTRACTION OF THE HOOF. 
Among other questions productive of heated argument 
come those relating to expansion of the horse’s hoof. In 
the past many observers have strenuously insisted on the 
fact that expansion and contraction regularly occur during 
progression. Opposed to them have been others equally 
firm in the belief that neither took place. Quite within 
recent times this question also has been settled once and for 
all by the experiments of A. Lungwitz, of Dresden. His 
conclusions were published in an article entitled ‘ Changes 
in Form of the Hoof under the Action of the Body-weight.’* 
In connection with this it is interesting to note how, all 
* Journal of Comparative Pathology and Therapeutics, vol. iv., 
p. 191. The whole of the matter in this article, from which we have 
borrowed Figs. 35 and 36, is too long for reproduction here. It forms, 
however, most instructive reading, and its careful perusal will well 
repay everyone interested in this most important question (H. C. R.). 
