40 NUTRITION OF FARM ANIMALS 



Similarly, plants contain a great variety of ingredients not 

 strictly belonging to any of the four main groups. In the 

 aggregate, these substances do not often add greatly to the po- 

 tential food value of feeding stuffs, but, on the other hand, 

 they may in some cases considerably modify their palatability 

 or the activity of the various processes of nutrition and so affect 

 the actual results of feeding. Until recently these secondary in- 

 gredients of feeding stuffs have received comparatively little 

 attention. 



69. Organic acids. Aside from the small amounts of free 

 fatty acids occurring in most native fats, both animal and vege- 

 table (29, 33), the acids of this series are seldom or never found 

 in native feeding stuffs. In those feeding stuffs which have 

 undergone bacterial fermentation, however, notably in the case 

 of silage, more or less acetic and butyric acids occur, but the 

 principal acid product of such fermentations is lactic acid, 

 C 3 H 6 O3. The same acids, along with formic and propionic 

 acids and minute amounts of ethyl aldehyde, likewise result 

 from the bacterial fermentation of the carbohydrates of the 

 feed in the paunch of ruminants and thus constitute a not un- 

 important portion of the non-nitrogenous material resorbed 

 from the feed (128-132). The principal organic acids found 

 in native feeding stuffs are malic, tartaric, citric and oxalic, 

 usually as the potassium, sodium or calcium salts. 



70. Ethereal oils. The so-called ethereal oils are substances 

 of complex molecular nature, somewhat resembling the true 

 oils in their physical properties but which can readily be dis- 

 tilled in a current of steam. Familiar examples are the so-called 

 oils of peppermint, lemon, anise, and the like. It is not known 

 that they have any direct nutritive value themselves but they 

 add to the flavor and aroma of feeds and in some cases are be- 

 lieved to stimulate the digestive processes. The agreeable 

 odor of good hay, for example, and doubtless in part its fa- 

 vorable dietetic effect, is due to substances resembling in prop- 

 erties the ethereal oils. To the same class of ethereal oils 

 belong the oils of mustard, onion and garlic, whose deleterious 

 effect upon the flavor of dairy products is so well known. 



71. Flavoring substances in general. What is called the 

 flavor of a food or feeding stuff depends largely upon the action 

 on the sense of smell of a great variety of substances either con- 



