21 
most of the reactions can have no great value for micros- 
copic investigation. With Millon's reaction, and the nitric 
acid and biuret tests the colour with very thin pieces of 
egg-white is very faint. 
With a minute object such as the protoplast of Spirogyra 
which in addition to protein contains also other substances, 
little is to be expected from the three last-mentioned 
reactions. In accordance with this I did not obtain favourable 
results, but the reaction with sugar and sulphuric acid 
yielded better ones. The objects were left in a sugar 
solution for some time and then sulphuric acid was allowed 
to flow in. Î[ used a mixture of 9 parts by weight of 
concentrated sulphuric acid and one part by weight of 
water, therefore sulphuric acid of 851/,°/,. 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. 
Àt 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 (KI. et V. N°. 41) and 
afterwards orange-red (KI. 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 Ï mention a reaction which is indeed not 
a real protein reaction, but which may sometimes serve 
for the indirect microchemical 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 precipitate with 
a tannin solution and can be used to demonstrate tannin 
microscopically. Î have not been able to confirm this and 
it is moreover in conflict with what is generally stated in 
chemical handbooks, namely, that a tannin solution is 
