1914] HOYT—COLLOIDAL METALS 207 
125 ppm. were fatal to only two kinds of the bacteria tested, while 
finely divided colloidal silver containing 70 ppm. was fatal to all 
the bacteria used in their investigations. Morse (13), from some 
preliminary experiments on several unicellular animals and plants, 
concluded that colloidal platinum and gutta percha are without 
appreciable effect on protoplasm. It should be noted that, in the 
present investigation, alga filaments in colloidal solutions often 
showed injury suddenly, after they had remained for several days 
in apparently excellent or good condition. 
The swelling of cell walls caused by akaline colloidal gold or 
platinum, as observed in these studies, seemed to-depend upon the 
presence of both the colloid and the alkali, since the walls seemed 
unaffected by the colloid alone and were very slightly altered by a 
solution of NaOH alone, while marked swelling was produced by a 
mixture of colloid and NaOH. A mixture of AuCl, and NaOH was 
without effect in this connection. The failure of colloidal silver to 
induce swelling may possibly be associated with those properties 
of this colloid that produced its toxic effect upon the protoplasm. 
That no sheaths were formed in those alkaline solutions of silver 
that permitted the alga to live in apparently good condition may 
be related to the extreme dilution of these silver solutions. 
Results strikingly similar to those obtained in the present 
Investigation from the use of colloidal gold and platinum with 
aOH were obtained by Kress (10) upon precipitating various 
substances (as calcium phosphate, copper sulphide, iron ferro- 
cyanide, alizarine-lead oxide) within the gelatinous sheaths of sev- 
eral species of Zygnema and other algae. Under these conditions 
there were formed colored, swollen, gelatinous masses, which 
Separated from the cells in a way quite like that described above. 
This swelling occurred not only on the walls of living cells, but also 
on the walls of cells killed by ether vapor or weak alcohol, although 
hot on the walls of those killed by corrosive sublimate, lead acetate, 
°r some other substances. Not all precipitates caused swelling, 
and the appearance of the gelatinous masses, when formed, differed 
With different precipitates and different species of algae. 
Since the formation of these swollen masses was caused only by 
Precipitates composed of small particles, while it was caused by 
