10 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



6. Dextrin. — Add iodine solution to solution of dextrin, and a reddish- 

 brown solution is produced. The colour disappears on heating and reappears 

 on cooling. 



7. Glycogen. — Solution of glycogen is given round : (a) it is opalescent 

 like that of starch. 



(6) With iodine it gives a brown colour very like that given by dextrin. 



The colour disappears on heating and reappears on cooling, 

 (c) By boiling with 25-per-cent. sulphuric acid for 15 to 20 minutes it is 



converted into grape sugar. 

 B. Lard is given round as an example of a fat. (a) It is insoluble in 

 water. 



(6) By boiling with potash it yields a solution of soap. 



(c) Add to this solution a few drops of 25-per-cent. sulphuric acid. On 



heating a layer of fatty acid collects on the surface. 

 (fZ) Shake up some lard with ether. It dissolves, leaving little or no 



residue. 



CARBOHYDRATES 



The carbohydrates are found chiefly in vegetable tissues, and 

 many of them form important foods. Some carbohydrates are, 

 however, found in or formed by the animal organism. The most 

 important of these are glycogen, or animal starch ; dextrose ; and 

 lactose, or milk sugar. 



They may be for the greater part arranged into three groups, 

 according to their empirical formulae. The names and formulae of 

 these groups, and the most important members of each, are as 

 follows : — 



The + and — signs in the above list indicate that the substances 

 to which they are prefixed are dextro- and levo-rotatory respectively 

 as regards polarised light. ^ 



The carbohydrates may be conveniently defined as compounds of 

 carbon, hydrogen, and oxygen, the two last-named elements being in 

 the proportion in which they occur in water. This definition is, 

 however, only a rough one, and if pushed too far would include 



' For a description of polarised light and polarimeters see Appendix. This and 

 the other matter in the Appendix are placed there for convenience, not because 

 they are unimportant. Students are therefore urged to refer to and carefully 

 study these subjects. 



