1334 
flow in. I used a mixture of 9 parts by weight of concentrated 
sulphurie acid and one part by weight of water, therefore sulphuric 
acid of 85/,°/,. This mixture has a much smaller carbonising action 
on the sugar than concentrated sulphuric acid and is therefore to 
be preferred. With small pieces of egg-white the reaction is very 
striking. At first the colour is red (compare Klincksieck et Valette, 
Code des Coleurs, 1908, N°. 16 and 21), sometimes with a very 
weak violet tint, then pure red (Kr. et V. N°. 41) and afterwards 
orange-red (Kr. et V. N°. 51). With very thin pieces the colour is 
still observable. The reaction is also very suitable for microchemical 
use. In Spirogyra the protoplasts are coloured a distinct light red, 
the nucleus with the nucleolus and the pyrenoids are darker. 
At this point I mention a reaction which is indeed not a real 
protein reaction, but which may sometimes serve for the indirect 
mieroehemical demonstration of protein, namely, the test with tannin 
and iodine in potassium iodide solution. In botanical papers I have 
found it stated that iodine in potassium iodide solution gives a pre- 
cipitate with a tannin solution and can be used to demonstrate tannin 
microscopically. I have not been able to confirm this and it is more- 
over in conflict with what is generally stated in chemical handbooks, 
namely, that a tannin solution is coloured violet by means of an iodine 
solution such as iodine in potassium iodide. Of course care must be 
taken that the violet colour is not masked by the addition of much 
iodine. In chemical books I have found no mention of a precipitate. 
When hide-powder or pieces of egg-white are brought into contact 
with a tannin solution, washed with water after some time and then 
treated with iodine in potassium iodide solution, they usually show 
a dirty brown colour; after repeated washing with water a fine 
violet colour (Kl. et V. 591, 596) appears, however. 
This reaction can also be applied to Spirogyra, but in this case 
the tannin solution is unnecessary, because Spirogyra itself contains 
tannin in solution in its cell-sap. The filaments of Spirogyra are 
warmed to 60° in water. They are then killed, the tannin leaves the 
vacuole and partly combines with the protein of the protoplast. If 
the filaments are now treated with iodine in potassium iodide solution 
and afterwards washed with distilled water until the iodine reaction 
of the starch disappears, it is then found that those parts of the 
protoplast which are rich in protein, are coloured violet. The nuclei 
with the nucleoli are finely coloured, the pyrenoids more faintly. 
I have been no more able to find protein in the intravital pre- 
cipitates with caffeine, antipyrine and ammonium carbonate than 
were Ar KrerRCKER, KrLEMM and Czaprk; neither when tbe precipitates 
