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 have been previously 

 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, 

 glycogeii, or certain proteins, 



2. Add iodine. A colour is produced : 



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

 at 40 C., or by boiling with dilute sulphuric acid. 



If reddish brown : Glyeogen 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, levulose, 

 maltose, lactose, and other reducing sugars (for distinguishing tests see 

 Lesson XIII.). 



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

 solution with 25-per-cent. sulphuric acid, and then boil with copper sulphate 

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

 by HC1 test (see p. 13). 



(c) Violet solution : Proteins (albumins, globulins, infra-proteins). In 

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

 magnesia. 



(d) Pink solution; biuret reaction. Peptones or 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 proteins 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. 



(b) No precipitate : Infra-proteins, 1 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 tempera- 

 ture of heat coagulation. 



1 The infra-proteins (see pp. 47 and 75) are by some called ' meta-proteins.' 



