FORM AND ACTION OF THE FOOT. 13 



structures witliin, wliicli are similarly prominent and 

 irregular in surface. (Figs. 9 and 10.) The first diagram 

 «liows a section through the point of the frog, the second 

 ■a, section through the cleft. 



The frog is fibrous, though not to such marked 

 degree as the other portions of the hoof. Its chief equali- 

 ties are elasticity and toughness. 



The Secreting Structures. 



If we macerate a dead foot in water for a week or 

 two, the hoof may be removed entire without injuring 

 the tissues within. In this way the sensitive foot or 

 *' quick " is exposed to view, and jjresents an exact coun- 

 terpa,rt of the inside of the hoof. The sensitive foot 

 consists of a layer of fibrous tissue' stretched over the 

 bones and other structures which form the centre of the 

 foot. It is plentifully supplied with blood-vessels and 

 nerves necessary to its double function as the source of 

 horn growth and as the tactile organ of the foot. Horn 

 is, of course, not sensitive, although the slightest touch 

 on a horse's hoof is recognized by the animal, and this 

 feeling is due to the impression made upon the sensitive 

 foot. In the living horse any injury to the "quick'* 

 <;auses the greatest pain, and, although this sensitiveness 

 is a serious disadvantage in disease, it is a most valuable 

 provision in health, enabling the horse, even through a 

 thick layer of horn, to recognize the quality of the sur- 

 face Tij^on which he may be standing or moving. It is 

 this sense of touch — this tactile function — which demands 

 that the sensitive foot should be so bountifully supplied 

 with nerves. 



Every farrier knows how profusely blood flows from 

 •any wound of the "quick " — evidence that the part is well 

 supplied with blood-vessels. This full supply of blood is 

 not merely for the ordinary waste and repair which 

 takes place in every tissue; it is to meet a special demand 

 — to supply the material for the production of horn. 

 The sensitive foot is the secreting structure of the hoof, 

 ■and the source of the constant growth and reproductioa 



