Hoyt: CULTURES OF SPIROGYRA _ 341 
no correction of the toxic conditions of ordinary distilled water. 
Heating in-an autoclave for 15 minutes at 144° C. made ordinary 
distilled water decidedly less injurious, but did not render it 
entirely nontoxic (III, 11). 
Dilution with an equal volume of physiologically pure water 
(III, 12) or with water from a vigorous culture of Nitella (III, 13) 
did not make the ordinary distilled water less toxic, but dilution 
with an equal volume of a colloidal platinum solution (III, 14) 
rendered this water less injurious.* 
The addition to ordinary distilled water, at the time of adding 
the alga, of filter paper (III, 15), cotton (III, 16), kaolin (III, 17), 
quartz sand (III, 18), or small amounts of chalk (III, 19, 20), 
produced no improvement; but the addition of abundant chalk 
(III, 21), lime (III, 25), broken agar sticks (III, 27), or dry 
sphagnum moss (III, 31) usually rendered the water nontoxic. 
Spirogyra filaments died within a few hours in ordinary distilled 
water to which a small amount of agar solution was added (III, 
28), they lived nearly two months on the surface of a 1 per cent. 
solution of agar made with this same water (III, 29), but died 
within three days on the surface of a 2 per cent agar solution 
(III, 30). In erdinary distilled water shaken with chalk (III, 22), 
wood charcoal (III, 23), or garden soil (III, 24) and decanted after 
the subsidence of the solid, little or no improvement was observed 
at first, but decided improvement was shown after a few days. 
Addition to the water of sediment from a vigorous culture of 
Nitella (III, 32) produced better growth than that occurring in 
untreated water, while sediment from the stock culture of Spiro- 
gyra (III, 33) produced no improvement. 
It was found that the alga filaments themselves may exert a 
profound influence upon the toxicity of the solution in which they 
are immersed. A transfer of filaments was made, in the usual 
manner, from the stock culture to a dish of ordinary distilled 
water (III, 34). These filaments were dead within eighteen hours. 
They were then removed from the culture and replaced by a new 
transfer of filaments from the stock culture. These also died 
within eighteen hours, and were replaced as before. The third 
* This colloidal platinum solution was kindly prepared by Dr. W. Fraenkel in 
the laboratory of Prof. G. Bredig. It contained 0.0096 g. of platinum per 100 c.c, 
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