DIGESTION AND NUTRITION 335 



number of factors which influence the completeness of 

 the process of digestion. Some of these factors are : 

 (i) Mechanical condition of the food, (2) combination 

 of foods, (3) amount of food consumed, (4) palatability 

 of the food, and (5) individuality of the animal. A di- 

 gestion coefficient is a variable factor capable of being in- 

 fluenced by these and other conditions. 



459. riechanical Condition. The mechanical condi- 

 tion of a food , as fineness of division and density of par- 

 ticles, materially influences digestion. As a general rule, 

 the finer the division the more complete is the digestion. 

 For example, experiments with pigs have shown that 

 wheat meal is 10 per cent, more digestible than whole 

 wheat. Experiments with other animals, recorded in 

 Bulletin No. 77, U. S. Department of Agriculture, Office 

 of Experiment Stations, giving the digestibility of Ameri- 

 can feeding-stuffs, show equally large differences. The 

 finer the division of the particles, the larger is the sur- 

 face exposed to the action of the digestive fluids. The 

 density of a material also influences its digestibility. Many 

 foods contain a fair amount of nutrients, but their me- 

 chanical condition is such that the nutrients are not easily 

 rendered available because of the presence of a large 

 amount of cellulose enclosing and protecting the nutri- 

 ents, and as a result, digestion and assimilation fail to 

 take place. This is particularly true of many coarse fod- 

 ders, as timothy hay and clover when allowed to become 

 overripe and fibrous. Digestion experiments with such 

 forage, and with that cut in early bloom, show that when 

 cut in early bloom, it is more digestible than when over-. 



