6 Composition and Nutritive Value of Straw. 



it contains. These, together with 'a small quantity of wax and 

 chlorophyle, seldom exceed 2 per cent., and are often less than 

 1 per cent. But it has been stated that straw contains as much 

 as 20 per cent, of fat, from a confusion between fat and fat- 

 forming matters a term sometimes applied to the whole group 

 of the non-nitrogenized substances. Such mistakes are often 

 disseminated by non-scientific men, who meddle with subjects 

 on which they are but imperfectly informed ; in which case their 

 theoretical deductions, resting on no sound basis, naturally do 

 not tally with the observations of practical men. Due account 

 being taken of the mischief which palpable errors in science 

 produce in the popular mind, it becomes as much the duty of 

 the scientific chemist to expose errors as to enrich our treasury 

 of chemical knowledge by fresh discoveries. 



Little need be said respecting the gum and mucilage in straw. 

 Their proportion, though not large, is appreciable, especially in 

 somewhat under-ripe samples, in which much more sugar is 

 likewise found than in over-ripe samples. Indeed, in the latter 

 the amount of sugar is scarcely appreciable. 



Cellular or woody fibre constitutes the bulk of straw, being, of 

 course, less valuable than any of the preceding constituents. 

 The various non-nitrogenized substances which enter into the 

 composition of straw contain, without exception, a large propor- 

 tion of carbon, for which reason they are sometimes called car- 

 bonaceous matter. Their use in the animal economy is of a 

 twofold character either to supply the materials for the forma- 

 tion of animal fait, or to support respiration and consequently 

 animal heat. These different carbonaceous substances are not, 

 however, equally well adapted to either of these uses, and may 

 be divided, according to the fitness and readiness with which 

 they fulfil the one or the other function, into 



1. Fat-producing substances. 



2. Heat-producing or respiratory substances. 



3. Indigestible substances. 



To the first belong the oil, fat, and waxy matter, which in 

 straw, as already mentioned, seldom amount to much more than 

 1 per cent. Oily and fatty vegetable substances are eminently 

 well adapted to the laying on of fat in animals, inasmuch as the 

 composition of vegetable fat is analogous if not identical with 

 the several kinds of fat found in the bodies of animals. The 

 fatty matters of food, without undergoing much change, are 

 therefore readily assimilated by the animal organism, and applied 

 when given in excess to the storing up of animal fat. On the 

 other hand, substances rich in starch are specially fitted to sup- 

 port respiration. Oily and fatty matters, however, when given 

 with a scanty supply of starchy food, become available for the 



