120 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



2. Maltose. — Maltose is the form of sugar which results from the 

 action of a diastatic ferment, or dilute acids with heat, on starches. It 

 resembles cane-sugar in many respects, but has the power of reducing 

 alkaline solutions of cupric hydrate, although its reducing power is one- 

 third less than that of dextrose. It rotates the plane of polarized light 

 strongly to the right, even more so than dextrose (+150°). It is capable 

 of undergoing fermentation, and, through the action of dilute acids with 

 heat, ma} r be converted into dextrose. It is this form of sugar which in 

 all probability invariably results from the digestion of the carbo-hydrates 

 in the animal body under the influence of an amylolytic ferment, and will 

 be again alluded to in the chapters on Digestion. 



3. Lactose, or Milk-Sugar (CjuHjjOu+HjO). — Lactose resembles 

 cane-sugar closely in its properties, but is more stable, and, like dextrose, 

 has the power of reducing the sugar tests. It rotates the plane of polar- 

 ized light to the right, the degree of the rotation diminishing with the 

 age of the solution. It is found only in milk; it crystallizes in hard, 

 white, rhomboidal prisms ; is soluble in six parts of cold and two and 

 one-half parts of hot water ; insoluble in alcohol, ether, and only slightly 

 sweetish. It is only fermentable with difficulty. It will again be alluded 

 to more at length under the subject of Milk. 



4. Arabin.— Arabin is capable of being converted by means of dilute 

 sulphuric acid into a sugar which is termed arabinose, and is closely 

 analogous to dextrose. It is the main constituent of gum arabic. ' It 

 polarizes light to the right, reduces the copper sugar tests, but is in- 

 capable of fermentation. 



II. Hydro-carbons, or Fats. — Fats may be either of animal or vege- 

 table origin, and occur either deposited within the interior of cells, or in 

 the form of solution or suspension in animal or vegetable juices. In the 

 animal body fat is especially formed in the cells of the connective-tissue 

 group, either through fatty degeneration of the protoplasmic cell-contents 

 of the connective-tissue corpuscles, or by the absorption of fat brought 

 to them by the cells by a vital process analogous to the feeding of the 

 amoeba, or the absorption of fat from the intestinal canal of animals. In 

 the formation of adipose tissue by either of these processes the proto- 

 plasmic cell-contents gradually become displaced, the nucleus lying 

 against the cell-membrane, while the cell-contents consist mainly of a 

 globule of oil. During the life of the organism the fatty contents of 

 cells are always of a fluid consistence, and, in the case of animals, only 

 solidify when cooled below a certain point, which is characteristic of 

 the different individual fats. In the vegetable cell the fats remain per- 

 manently fluid, with but few exceptions, in the form of oils. As animal 

 fats solidify, a partial process of crystallization into groups of acicular 

 crystals often takes place. When within the interior of cells fats are 



