28 
When Spirogyra is washed out and then disintegrated, 
the mass has a faint acid reaction to litmus paper but a 
solution of gallnut-tannin and of Spirogyra-tannin are 
likewise acid. À suitable microchemical method for de- 
monstrating free acids in the cell-sap, does not appear to 
exist. No value can be attached to Loew and Bokorny's!) 
method. They lay filaments of Spirogyra in a potassium 
iodide solution and seeing that no iodine is set free, they 
infer the absence of free acid in the cell-sap. The liber- 
ation of iodine by free acid cannot be explained chemically, 
for although dilute acids might set free hydriodic acid 
from potassium iodide, they cannot liberate iodine. 
Ï attempted to demonstrate free acid in the living cells 
of Spirogyra as follows. I placed Spirogyra in a solution 
of potassium iodide (0.1 °/;) and of potassium iodate 
(0.025 °/;), but no separation of iodine by free acid was 
indicated (5KI + KIO, + 6HCI — 6KCI + 61 + 3H,0). 
On heating Spirogyra for some time in a 0.1 °/, solution 
of citric acid, before placing it in the solution of potassium 
iodide and iodate a very faint blue colour in the starch 
and faint violet coloration of the nuclei was to be seen; 
the latter had taken up tannin from the cell-sap, for in 
the meantime the cells had perished. This result points 
to light absorption of citric acid and separation of iodine 
by this acid. The method seems to yield useful results 
and probably in the first experiment iodine would also 
have been liberated, in case Spirogyra contained free acid. 
It should be noted that Spirogyra is very sensitive to 
dilute solutions of organic acids. In a 0.1!°/, solution of 
citric acid, tartaric acid, malic acid, quinic acid, it quickly 
dies. 
On these grounds it is very improbable that Spirogyra 
1) O. Loew and Th. Bokorny, Ueber das Vorkommen von activem 
Albumin im Zellsaft und dessen Ausscheidung in Kôrnchen durch 
Basen. I. c. 
