THE CONSTITUENTS AND USES OF FOOD. 



lose is that of starch. Fibre is not an homogeneous and uniform 

 substance, but a varying mixture of cellulose with a complex 

 body or bodies, called lignose or lignin, related to the aromatic 

 series. In the following pages we use the term "fibre" as a 

 convenient designation for that part of the food-grain which is 

 neither albuminoid, nor oily, nor starchy, which resists the solvent 

 action of boiling alkaline and acid solutions, and which is un- 

 affected by alcohol and by ether. It contains both cellulose 

 and lignose (sometimes cutin), but however variable and mixed its 

 composition it may be safely affirmed to be wholly useless as 

 food. In actual foods it is indeed often worse than useless, lock- 

 ing up in an inaccessible condition a part of the albuminoids, 

 the oil, and the mineral matter of the seed or grain. 



Oils and F.its* The vegetable oils and fats, while insoluble 

 in water hot or cold, are readily dissolved by liquids which 

 are themselves not miscible with water, such as benzene, pe- 

 troleum-oils, and ether. They are distinguished from the 

 volatile oils by their leaving a permanent translucent trace on 

 paper, and by their fixity at ordinary temperatures. Very few 

 of the seeds discussed in the present Handbook contain so much 

 oil that it can be extracted by simple pressure ; the pea-nut 

 (p. 127) is an exception. The fixed vegetable oils and fats con- 

 sist of certain chemical compounds called glycerides, associated 

 with small quantities of substances known as " fatty acids." 

 The glycerides themselves may be regarded as glycerin, plus 

 one or more fatty acids, and minus water. While starch and 

 sugar contain hydrogen and oxygen in the exact proportions to 

 form water, oils contain an excess of hydrogen. From this 

 cause, and from their greater richness in carbon, a given weight 

 of oil will give out more heat, or set free more energy when 

 burning, than the same weight of starch or sugar. The fol- 

 lowing table shows the percentage composition of the oils 



* These are sometimes called "hydrocarbons" by writers on dietetics; this is 

 incorrect and misleading. True hydrocarbons contain hydrogen and carbon 

 only, and are absolutely indigestible and useless as food. 



