134 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



DETECTION OF PHYSIOLOGICAL PROXIMATE PRINCIPLES 



Subsequent lessons may be very usefully employed by the class in testing 

 for the various substances the properties of which they have studied. The 

 following scheme will form a rough guide to the tests to be employed for 

 the most important of the proximate principles : — 



1. Note reaction, colour, clearness or opalescence, taste, smell. Coloured 

 liquids suggest blood, bile, urine, &c. Opalescent liquids suggest starch, gly- 

 cogen, or certain proteids. 



2. Add iodine. A coloiir is produced : 



If blue : Starch. Confirm by converting into a reducing sugar by saliva 

 at 40° C, or boiling with dilute sulphtiric acid. 



If reddish brown : Glycogen or dextrin. Glycogen forms an opalescent 

 solution in water, and is readily precipitated by alcohol. It is precipitated by 

 basic lead acetate. Dextrin forms a clear solution : it is not precipitated 

 by basic lead acetate unless ammonia is added also. It is not precipitated by 

 alcohol unless a large excess is added. Both dextrin and glycogen are, like 

 starch, convertible into a reducing sugar. 



3. Add copper sulphate and caustic potash. 



(a) Blue solution : boil ; yellow or red precipitate. Dextrose, maltose, or 

 lactose (for distinguishing tests see Lesson XIII.). 



(6) Blue solution ; no reduction on boiUng ; boil some of the original 

 solution with 25 per cent, sulphiu-ic acid, and then boil with copper sulphate 

 and caustic potash ; abundant yellow or red precipitate : Cane sugar. Confirm 

 by HCl test (see p. 9). 



(c) Violet solution : Proteids (albumins, globulins, albuminates). In 

 presence of magnesium sulphate the potash causes also a white precipitate of 

 magnesia. 



(d) Pink solution ; biuret reaction. Peptones or albumoses (proteoses). 

 In presence of ammonium sulphate very large excess of potash is necessary 

 for this test. Only a trace of copper sulphate must be used. 



4. When proteids are present proceed as follows : Boil the original solution 

 (after adding a trace of 2-per-cent. acetic acid). 



(a) Precipitate produced : Albumins or globulins. 



(6) No precipitate : Albuminates, proteoses, or peptones. 



5. If albumin, or globulin, or both, are present, saturate a fresh portion with 

 magnesium sulphate or half saturate with ammonium sulphate ; filter ; the 

 precipitate contains the globulin, the filtrate the albumin. Test temperature 

 of heat coagulation. 



