S Feb., 1907.] l-'.lcDwnts of Animal Physiology. 83 



the fatter the animal the lower is the ash content. Thus, the ash of an 

 ox will vary from 6 — 4.4 per cent., a sheep from 4 — 3 per cent., and a pig 

 from 3 — 2 per cent. 



The following table gives an idea of the percentage amount b\- weight 

 of ash in different parts of the animal body : — 



Per cent. Per cent. 



Hair and brain ... 0.5 — 0.7 Cartilage ... ... 1.5 — 2 



Blood ... ... 0.6 — I Bone ... ... 6 — 7 



Muscle ... ... i — 1.5 Enamel of tooth ... 96 — 98 



Carbohydrates. 



Carbohydrates are compounds of carbon, hydrogen, and oxygen, the 

 last two elements being present in the same proportion as in water — hence 

 the name. All carbohvdrates can be burned in the presence of oxygen, and 

 when thus treated yield two end-products of combustion, namely, water and 

 carbon dioxide. The absence of nitrogen is always to be borne in mind. 



It is usual to classify the carbohydrates into the following groups: — 



Simple sugars, or Monosaccharides. 



Compound sugars with two sugar components, or Di saccharides. 

 Compound sugars with three sugar components, or Trisaccharides. 

 Carbohydrates compounded of a large number of sugar components, 

 or Polysaccharides. 



MONOSACCHARIDES. — These bodies are all soluble in water, are 

 sweet to the taste, and can be prepared in the form of white crystals. They 

 not only burn w^hen heated in the presence of air, but also combine with 

 oxygen when in solution. This property is strikingly shown in the follovr- 

 ing simple experiment: — If to a, few drops of copper sulphate (bluestone) 

 solution some strong caustic potash is added, the colour gets slightly deeper 

 and a faint flocculent precipitate of copper hydrate is formed. Boiling 

 produces no change, but if a little glucose solution is added whilst hot, a 

 copious red precipitate forms, due to the sugar robbing the copper hydrate 

 of some of its oxygen. A large number of monosaccharides is known to 

 the chemist, but only a few of them have any physiological importance; 

 these few can now be taken in series. 



1. Dextrose, called also glucose or grape sugar. It is present, as 

 the third name implies, in the juice of the grape. It is also found in the 

 blood, in honey, in various vegetable juices, and in the urine of diabetic 

 animals. It is prepared on a large scale by Ixiiling starch with weak 

 sulphuric acid. Dextrose ferments readilv with yeast, producing alcohol 

 and carbon dioxide. 



2. Levulose, called also fructose or fruit sugar. Tliis sugar is 

 found associated with dextrose, in honey and in manv plant juices. It 

 cannot be so readily crystallized as dextrose, and is .much more difficult to 

 prepare ; in consequence it is a much more expensive article to purchase. 

 Like dextrose, it ferments w ith vea.st, producing alcohol and carbon dioxide. 



3. Galactose, which is important on account of its relation to milk 

 sugar, to be discussed later. With yeast it ferments either very slowly or 

 not at all. 



4. The Pentoses. — This group comprises sugars which, though they 

 are not found free in nature unless in exceptional circumstances, had better 

 be mentioned here. They contain in their molecules less carbon. less 

 hydrogen, and less oxygen than the three monosaccharides given above, and. 



