1918-19.] On the Mode of Action of Metal Sols. 
147 
Colloid. 
Percentage 
of Silver. 
Rotation of 
analysing Nicol 
for Violet. 
Rotation of 
analysing Nicol 
for Green. 
Number of 
visible 
Submicrons. 
A, 50 per cent. ! 
0*002 per cent. 
79*5° 
73*0° 
14 x 10 6 
B, 50 „ 
0*0027 
complete 
73*2° 
lOxlO 5 
0, 25 „ 
1 [ 
0*0014 
76*8° 
61-6° 
5 x 10 5 
It is evident that colloid B contained a much larger number of so-called 
amicrons than colloid A. It was found to be more powerful as a bactericide 
and antiseptic. 
Bacillus typhosus (10 millions per cb.mm.). 
Colloid. 
15 Minutes’ 
30 Minutes’ 
Exposure. 
Exposure. 
A, 0*004 per cent. Ag . 
+ 
0 
B, 0*0027 „ 
+ 
0 
The difference in their action was much more marked in the antiseptic 
series of experiments. Those with B. paratyphosus A, which was the 
most concentrated bacillary emulsion used (34 million organisms per cb.mm.), 
may be given as an example. 
Bacillus paratyphosus A. 
Colloid. 
18 Hours’ 
Incubation. 
f 
66 Hours’ 
Incubation. 
A, 0*002 per cent. Ag . 
+ 
B, 0*0004 
0 
+ 
B, 0*0008 
0 
+ 
B, 0*001 
0 
0 
Similar results were obtained with other organisms It would therefore 
seem that the chief, if not the whole, activity of silver colloids in antiseptic 
experiments in vitro is to be ascribed to the ultramicroscopic particles 
below 15 fxjj, in diameter. And since particles below 5 /xyu. in diameter 
have no influence on the polarisation and therefore probably the scattering 
of light, a pharmacological effect must be attributed to silver particles 
between 5 /ul/ul and 15 fxfx in diameter. Cernovodeanu and Henri also came 
to the conclusion that the smallest particles were the most active. They 
