646 A MANUAL OF VETERINARY PHYSIOLOGY 



the base. The horse in draught allows his weight to act as a 

 falling body, but it would be of no mechanical value if it fell verti- 

 cally ; it has to fall obliquely, and to secure this the feet are employed 

 as a means of purchase, while the body is kept on the move. 



In ordinary draught- work simple pressure against the collar 

 suffices to move the load, but where the latter is considerable the 

 animal gets closer to the ground, bending both knees and hocks 

 in order to obtain a foothold, and pressing forward from the hind- 

 feet especially on starting. In starting a heavy load the diaphragm 

 is fixed, the abdominal muscles tense, those of the hind-quarters 

 so shortened that the skin over them is thrown into ridges ; the- 

 muscle tensing the fascia of the thigh stands out like a cord, and if 

 ascending a hill, the toes of the fore-feet are turned in, perhaps in 

 order to increase the size of the chest by turning out the elbows. 

 In heavy draught body weight tells, and with well-made horses 

 body weight and height go together. The increase in body weight 

 for increase in height may generally be considered to be 1 hundred- 

 weight for every 4 inches (1 hand) ; so of two horses, one of 15 and 

 the other of 16 hands, all other things being equal, the latter should 

 be able to exert a force in draught roughly 112 pounds greater than 

 the other. Neither height nor weight govern the indefinable 

 quality of spirit and determination. Of two horses of equal weight 

 and similar build, one may be invaluable, the other worthless, as 

 a worker. 



The strain in heavy draught is not confined to the limbs ; it is 

 impossible for a horse to start a weight unless the muscles of the 

 back and loins are fit, and it is equally impossible for him to stop 

 it unless these parts are in sound working order. In heavy draught- 

 work on the level it may sometimes be noticed that the toes of the 

 fore-feet are the first to make contact with the ground. This is due 

 to the animal being unable to extend his shoulders properly owing 

 to the load. Though the horse is designed to drag weight, he 

 only drags it well on a level. Uphill his power rapidly diminishes, 

 owing to the effort required to carry his own body weight. If, for 

 example, he hauls one ton on the level with an expenditure of 

 60 pounds, he will require to exert a force of 223 pounds to ascend 

 a hill of 1 in 14, and this increase is made up of 156 pounds for the 

 load, and 67 pounds to counteract the gravity of his own body weight. 

 So badly, indeed, does a horse climb a hill with a load, that Desagu- 

 liers* stated that, if the hill be steep, three men, each carrying 

 100 pounds, will ascend it faster than a horse dragging 300 pounds. 

 Telford showed that, where possible, 1 in 40 should be the maximum 

 inclination of the road ; anything over that greatly increased the 

 work of the horses. One in forty is the angle of repose — viz., the 

 steepest acclivity down which a vehicle will not roll of its own 

 gravity. 



Strength of Horses. — A comparison between the strength of a horse 

 and that of a man has frequently been made, and the amount 

 variously stated at from five to seven men. We have found that 

 most horses weighing about \ ton will just pull seven men 

 along, but in the case of a notoriously powerful draught -horse, 

 weighing 14 hundredweight, his strength was equal to thirteen men, 

 whom he dragged very slowly along. This, however, is most 

 exceptional. The greatest force a horse can exert for a few seconds 



* ' A Course of Experimental Philosophy,' 1763. 



