1914] HOYT—COLLOIDAL METALS 199 
second and third days many filaments were injured, while on the 
fourth day practically all were dead. 
Diluting the gold solution with an equal volume of non-toxic 
water produced no improvement. In such a solution Spirogyra 
from the stock culture remained in excellent condition one day, but 
on the second day about half of the filaments were dead (II, 5c). 
The effect of transferring portions of Spirogyra from colloidal 
gold solution to non-toxic distilled water was tested. Filaments 
which had been in gold solution for two days, when placed in this 
water, showed injury within one day and were, for the most part, 
dead within two days, while the portions of the alga remaining in 
the gold solution were still in excellent condition. Other effects of 
such transfers will be described later. 7 
Although the colloidal gold solution itself was only slightly 
injurious, the sodium hydrate solution (about 0.02 per cent) used 
in its preparation was extremely toxic, killing all the filaments and 
causing contraction of their cell contents within 17 hours (II, 6). 
This alkaline water, when diluted with an equal volume of non- 
toxic distilled water, was still decidedly toxic (II, 7), but was not 
injurious during the period of the experiment (5 days) when 
diluted with an equal volume of the full strength colloidal platinum 
solution (II, 8). A similar improvement by the addition of 
colloidal platinum was produced on 0.02 per cent and 0.01 per cent 
solutions of NaOH prepared at another time (II, 10, 12). Even 
weak solutions of silver seemed to produce a beneficial effect on this 
alkaline solution, since the alga lived better with the addition of 
®-0I-9.005 per cent of the full strength silver solution (0.009- 
°-0045 ppm.) than in the NaOH solution alone (II, 9). The 
addition, however, of 0.01 per cent of AuCl, to 0.02 per cent and 
0.01 Per cent solutions of NaOH produced no improvement in these 
solutions; on the contrary, the soluble gold salt seemed to make the 
NaOH solutions more injurious (II, 10, 11). 
The colloidal solution of platinum was still less injurious than 
that of gold, filaments of S pirogyra placed in this solution remaining 
apparently perfect condition for g days and dying only after 22 
days (IIL, 13). Not only was this platinum solution not injurious 
during the first few days of the experiments, but it produced 
