

248 MR. S. LE M. MOORE'S STUDIES 



and a light red precipitate forms at junction of acid and solution: 

 soon on the rest of the overlying liquid a pink colour appears, 

 which after some hours becomes brown-pink. 



(C). "With Copper Sulphate a grey precipitate, becoming 

 brown on boiling with Caustic Potash. 



Hence with Catechu, (M), (X), and (E) succeed : (C) fails, 

 and this latter may therefore be employed as a crucial test : as the 

 sequel will show, it also fails with cell-walls. 



To Krasser's list, therefore, we must add, as giving (X), tannic 

 acid: as giving (M), (X), and (R), a solution of Catechu. 



One may also mention here G-nezda's # test for proteids — a 

 solution of Nickel Suiphate charged with Ammonia. To various 

 proteids studied by G-nezda it gives a blue or a yellow colour, 

 the blue becoming yellow, the yellow orange on addition of 

 caustic potash. Tannic acid gives with this a flocculent dirty 

 pink precipitate, not changing with caustic potash : catechu a 

 slight brown precipitate, which on pouring in caustic potash 

 becomes flocculent and somewhat paler in colour. 



Hence this test also fails with the tannins, and so should 

 furnish evidence of a crucial character. 



Cell-walls giving Proteid Reactions will give Tannin 



Reactions as well. 



If now our cell-walls, supposed, by yielding proteid reactions, 

 to contain proteid, will give tannin reactions as well, we have a 

 strong confirmation of the idea that tannin and not proteid is the 

 substance we are in quest of. But before going further into this 

 matter, it is necessary to remind the reader that the colours one 

 recognizes in thin sections under the microscope through strong 

 transmitted light must vary somewhat from those seen in making 

 test-tube experiments. Thus, browns will tone off to yellows as 

 the section becomes thinner; reds to pale pink and greens 

 towards yellow, while grey will tend to become invisible, and 

 so on. 



It must be premised that, as the reader is doubtless aware, 

 tannic acid gives with iron salts a blue-black and catechu a green 

 precipitate. "With both, Nessler's fluid (test for Ammonia) 

 gives a brown precipitate, and potassium bichromate does the 

 same with a solution of tannic acid, catechu striking a warmer 



Proc. Roy. Soc. vol. xlvii. (1890). 



