108 VETEEINAEY HYGIENE 



the ox and sheep, the digestion of the horse is as a rule 

 inferior to ruminants in the matter of cellulose, fat, and 

 carbo-hydrates, while in the matter of proteids he holds 

 his own. 



Before proceeding to describe the causes influencing the 

 digestibility of certain foods, it is desirable to consider the 

 question of the digestion of cellulose. 



Cellulose Digestion. — The horse, ox, and sheep can digest 

 cellulose, the pig and human subject are practically unable 

 to deal with it. The cellulose is mixed up with the other 

 fibre in the food, but either by the process of decomposition 

 brought about by organisms in the digestive canal, or by 

 the presence of a cellulose dissolving ferment — which has 

 never been isolated — a certain proportion varying from 

 30 to 70 per cent, in different animals is rendered soluble, 

 and is pure cellulose having the same composition as starch. 



There is great difference of opinion as to whether the 

 cellulose when isolated is of much economic value. Experi- 

 ments on the horse conducted with great care show it to be 

 useless for the purpose of work. Other observers have 

 stated that it exercises an economical influence over the 

 destruction of proteid. 



Fermenting cellulose yields 60 per cent, of fluid fatty 

 acids, butyric and propionic, while a smaller quantity is 

 given off as marsh gas and carbonic acid. Neither the 

 fatty acids nor the marsh gas can be of any use in nutri- 

 tion, so that observers believe that not half the cellulose 

 dissolved can have the same function as starch. 



The view at present adopted is that ruminants are prob- 

 ably able to utilize cellulose to better effect than the horse, 

 and that with the latter the most careful observations 

 appear to show that for the production of work cellulose is 

 useless. 



Before entirely accepting this position, our knowledge of 

 cellulose must be advanced, at present we know extremely 

 little about it, and it seems a waste of energy for a digestive 

 system to be able to dissolve a food substance, and yet not 

 to be able to utilize it. 



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