420 THE KXTEh 'OR OF THE HORSE. 



it from another charged jar, and thus appreciate the difference of their 

 internal condition ; the simple examination of the external form will 

 be no criterion to us. 



The same conditions exist for endurance. Until now, we have 

 considered it only as a total or a product. The study of the conforma- 

 tion may, of course, cause us to suspect its existence ; experiment alone 

 is capable of proving it. Now, among horses (pardon this metaphor) 

 there are so many empty Leyden jars that one is of necessity compelled 

 to touch and to test them, in order to avoid the inconveniences resulting 

 from purchasing them. 



Practical Determination of Endurance. — In what way shall 

 we make a practical determination of endurance? Evidently, by sud- 

 denly increasing the expenditure and pushing the animal's work as 

 much as possible. In the draught-horse, for example, it can be proved 

 by making the animal pull a heavy load up a hill at a fast walk. In 

 the fast horse, by obliging him to pull or carry a somewhat heavy' 

 weight at an unusually fast gait, the trot or the gallop. 



It is well understood that these kinds of experiments should 

 never be carried to the point of becoming prejudicial to the animals. 

 Hence, in order to render the experiment less severe, without making 

 it, on that account, less decisive, it is important to examine the condi- 

 tion of the respiration. What takes place in the muscles and, for still 

 greater reason, the nervous centres cannot be seen ; but, as the contrac- 

 tion supposes a proportionate excitation and circulation ; as, besides, the 

 blood before returning to the muscles is obliged to pass through the 

 lungs and to absorb from them as much material as it gives off, the 

 result of this is that the activity of the thoracic belloics is in close cor- 

 relation with the amount of the work, the quantity of tissue- waste, 

 and the degree of fatigue. It follows from this that difficult breathing 

 shows to the observer the state of exhaustion, and gives him a knowl- 

 edo-e of the reserve strength which the animal still has at his disposal. 

 It is true, then, that the flank is to the horse as the manometer is to 

 tlie steam-engine, since it indicates the tension of the functional activity 

 of the horse, as the manometer indicates that of the steam. 



As to the nerve conductibility, its feebleness or its disappearance is 

 seen in unequivocal signs on the locomotory apparatus : the muscular 

 contractions are weaker and slower ; the efforts diminish in intensity 

 and rapidity ; the intervals between the steps are no longer equal and in 

 co-ordination ; the members meet and strike each other ; the gait, at first 

 uncertain, becomes tottering ; the head hangs low ; the subject becomes 

 more and more insensible to the surroundings ; soon he falls in a heap 



