ANIMAL MOTORS 



If the road surface be inclined, it will be found that 

 the line of least draft is nearly parallel to the road surface. 

 If the trace is inclined upward from the line of least 

 draft there is a tendency to lift the load; if the line of 

 draft is inclined downward there is a tendency to press 

 the load on the surface. Furthermore, it is found that 

 roads are not perfectly level and there are obstructions 

 over which the wheels of vehicles must pass, or, in other 

 words, the load at times must pass up a much greater in- 

 cline than a general slope indicates, and hence this calls 

 for a greater angle of trace than will be needed for level 

 or smooth road. Teamsters find in teaming over roads 

 in one locality that they need a different angle of trace 

 than they find best in another, because the grades of the 

 roads are different. 



410. Width of hock. As mentioned before (405) prac- 

 tically all of the pull a draft horse exerts is thrown upon 

 his hind legs and for this reason the form and strength 

 of this part must be considered in the selection of a horse 

 for draft purposes. If the hock is wide or, in other words, 

 if the projection of the heel bone beyond the joint is 

 large, the muscles will be able to straighten the limb 

 under a greater pull than if the projection is small; thus 

 the ability of the horse to overcome resistance will be 

 increased. Thus there are many things to be considered 

 in the selection of a draft horse. The general make-up of 

 a horse built for speed is notably different from one built 

 for draft purposes. 



411. The horse at work. When a horse is required to 

 exert the maximum effort, it is necessary to add to his 

 adhesion or grip so that he may be able to exert his 

 strength to a limit without any slipping or without a 

 tendency to slip. But if the horse is loaded all the time, 

 either by a load upon his back or a low hitch, he is at 



