CHAP. XIII.] DIGESTION IN THE HORSE. 477 



large ; moreover very large quantities of saliva are secreted and 

 added to the dry food which is swallowed. We may assume that a 

 horse of average size and weight will require, in order to keep in a 

 state of nutritive equilibrium, about 7'5 kilo, of hay and 2'27 kilo, of 

 oats, or if fed on hay alone at least 10 kilo. (22 Ibs.); according 

 to Colin's calculations, the saliva secreted by a horse during the 

 mastication of a meal of 4 kilo, of hay amounts to 16 kilo, so that 

 the daily food would, on this supposition, require 40 kilo, of saliva ; 

 in other words, the total weight of dry food and saliva entering 

 the stomach during twenty-four hours would be 50 kilo. But to 

 this we must add a quantity of water drunk, which cannot be esti- 

 mated at less than 10 litres, so that the total ingesta mixed with 

 saliva entering the stomach of the horse may be estimated as 

 weighing about 60 kilo, or 132 Ibs. per diem. When we reflect, 

 further, on the bulk occupied by a quantity of hay weighing 22 Ibs., 

 we shall have an adequate explanation of the capacity of the alimen- 

 tary canal of the horse. Taking now the case of the ox, we may 

 calculate that if fed upon hay alone it would consume, on an average, 

 about 15 kilo. (33 Ibs.), with which would be mixed 60 kilo (132 Ibs.) 

 of saliva and from 15 to 25 litres of water, so that from 90 to 100 

 kilo, of matter would enter the rumen per diem. 



' The stomach of the horse is remarkable for its small size both in 

 relation to the rest of the alimentary canal and to the large amount 

 of food which the animal consumes. Thus while the stomach of a 

 large dog may have a capacity of 6 litres, that of a horse may not 

 contain more than from 10 to 18 litres 1 .' The comparative small- 

 ness of the stomach is connected with the fact that when the 

 food consumed is hay or straw, its stay in the stomach is, for the 

 most part, a short one. In the horse, as in other herbivorous animals, 

 under normal conditions the stomach at the commencement of a 

 meal usually contains considerable quantities of undigested residues 

 of previous meals. The newly ingested food partly forces out of the 

 stomach some of the residual food which it contained, and partly 

 becomes mixed with another portion of the residue. From the very 

 commencement of the meal, however, some of the contents of the 

 stomach pass through the pylorus into the duodenum. The quantity 

 escaping does not, however, equal that which enters, so that the 

 stomach gradually becomes distended. When a certain point is 

 reached, however, the quantity admitted into the stomach is balanced 

 by the quantity leaving it, so that the volume of the organ remains 

 the same as long as the animal continues to eat. The meal finished, 

 the passage of the contents of the stomach into the duodenum 

 becomes materially slower, and it is only after many hours that the 

 stomach can empty itself. When the aliment consumed is composed 

 of oats, the process of gastric digestion is one which lasts longer, and 

 which more nearly approaches that which goes on in the stomach of 

 man or the carnivora. 



1 J. G. McKendrick, A Text-book of Physiology, 1889, see Vol. 11. p. 99. 



