DIGESTION 193 



tins formation of sugar ? It has been shown that oats may 

 yield a starch-converting ferment, and the view that the grain 

 provides its own enzyme for the conversion of starch into sugar 

 may be provisionally accepted as the explanation of the presence 

 of sugar in the stomach of the horse. The whole of the starch 

 is not thus converted, for distinct evidence of unaltered starch 

 can be obtained in the first portion of the small intestines. 

 Further, some of the starch is no doubt converted into lactic 

 acid, and the presence of this acid in the proportion of 2 per cent, 

 does not in any way inhibit the amylolytic action. If oats provide 

 their own starch-converting enzyme, we see the strongest argu- 

 ment against boiled food for horses — a practice we believe to be 

 deleterious, or even dangerous. 



Fats are not acted upon in the stomach, though the envelope 

 surrounding the fat globule is digested, and the fat set free. 



Cellulose fermentation is considered by Tappeiner to occur in 

 the left sac of the stomach, and when marsh-gas has been found 

 in this organ, it results from cellulose decomposition. Brown* 

 has shown that the destruction of the cell wall of oats and barley 

 occurs in the stomach, where it is dissolved by a cyto-hydrolytic 

 ferment pre-existent in the grain ; the changes occur with extra- 

 ordinary rapidity in the stomach of the horse. The researches 

 of this observer on a cellulose-dissolving ferment are of the 

 greatest interest to the veterinary physiologist, and of consider- 

 able practical importance. 



Periods of Stomach Digestion in the Horse. — Stomach digestion 

 in the horse has been divided by Ellenberger and Hofmeister 

 into certain periods corresponding to definite chemical changes 

 in the food. For example, it is said that during the two first 

 periods, which between them last two and three hours, starch 

 conversion, lactic acid fermentation, and proteid conversion to 

 a limited extent occur. In the third period mixed digestion of 

 starch and protein occurs, while in the fourth and last period 

 only protein digestion takes place. The third and fourth periods 

 may together last four hours and upwards. We must be careful 

 to avoid regarding these periods as based on some rigid law ; 

 they are very variable in duration, due to causes we have pre- 

 viously considered, and run imperceptibly into each other. 

 With this caution we give the following periods at which gastric 

 digestion is said by Ellenberger and Hofmeister to be at its 

 maximum in the horse : 



After a moderate feed digestion is at its height in 3 or 4 hours, 

 full „ „ „ „ 6 to 8 „ 



„ an immoderate „ delayed still longer. 



* ' On the Search for a Cellulose-dissolving Enzyme,' H. T. Brown, 

 F.R.S., Journal of tlie Chemical Society, 1892, p. 352. 



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