APPENDIX. 339 



(a) Glycogen (C 6 H 10 6 ). This substance, which is identical in com- 

 position with starch, and like it, is readily converted into sugar by fer- 

 ments, is found in many embryonic tissues and in all new formations 

 where active cell-growth is proceeding. It is present also in the pla- 

 centa. After birth it is found almost exclusively in the liver and muscles. 



Glycogen is formed chiefly from the saccharine matters of the food; 

 but although its amount is much increased when the diet largely consists 

 of starch and sugar, these are not its only source. It is still formed 

 when the diet is flesh only, by the decomposition, probably, of albumin 

 ID to glycogen and urea. 



The destination of glycogen has been considered in a former chapter. 

 (Seep. 282, Vol. I.) 



(b) Glucose or grape sugar (C 6 H 12 6 -J- H 2 0) is found in minute 

 quantities in the blood and liver, and occasionally in other parts of the 

 body. It is derived directly from the starches and sugars in the food, or 

 from the glycogen which has been formed in the body from these or other 

 matters. However formed, it is in health quickly burnt off in the blood 

 by union with oxygen, and thus helps in the maintenance of the body's 

 temperature. Like other amyloids it is one source whence fat is derived. 



(c) Lactose or sugar of milk (C 12 H 22 O u -}- H 2 0), is formed in large 

 quantity when the mammary glands are in a condition of physiological 

 activity, human milk containing 5 or 6 per cent, of it. Like other 

 sugars it is a valuable nutritive material, and hence is only discharged 

 from the body when required for the maintenance of the offspring. The 

 same remark is applicable to the other organic nutrient constituents of 

 the milk, albumin and saponifiable fats, which, if we except what is 

 preseni in the secretions of the generative organs, are discharged from 

 the body only under the same conditions and in the same secretion. 



(d) Inosite (C 6 H J2 6 -f- 2 H 2 0), a variety of sugar, identical in com- 

 position with glucose, but differing in some of its proparties, is found 

 constantly in small amount in muscle, and occasionally in other tissues. 

 Its origin and uses in the economy are, presumably, similar to those of 

 glycogen. 



(e) Maltose (C 12 H 22 O n ), is formed in the conversion of starch into 

 glucose (see p. 336, Vol. II. j. 



(3.) ORGANIC ACIDS. 

 Group I. Monatomic Fatty Acids. 



Formic HO OH 



Acetic C 2 H 3 OH 



Propionic . . . . C 3 H r OH 



Butyric . . . . C 4 H^ OH 



Valerianic . C. H Q OH 



Caproic . . . -. C 6 H n OH 



Capric . . . . C 8 H OH 



Palmitic . . . . 16 H 31 OH 



Stearic .... C 18 H 3B OH 



Oleic CL H,, OH 



