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 striae (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 papillae 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 CONTEACTION 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.). 



