14 
in the above experiments was between 1:200 and 1:100, while further 
and similar experiments showed that a percentage of 1:125 inhibits 
bacterial growth for 21 days, but a growth occurred on the fourteenth 
day in a percentage of 1:150. 
It must be remembered that the antiseptic property of a substance 
varies more or less with light, character of medium used, and the tem- 
perature, the relative importance of these factors increasing in the 
order named. The intiuence of diHused light is comparatively feeble. 
The condition of the medium, independent of the presence of the sub- 
stance whose antiseptic value is being determined, is an influential 
factor. A strongly alkaline or acid medium is usually inimical to the 
growth of bacteria, and the nutrition may not be favorable for the 
development of the micro-organisms present. A low temperature will 
inhibit bacterial growth and a high one destrov bacterial life. 
Experiments were performed with sewage to determine the quantity 
of zinc chloride necessary to prevent the development of bacteria. A 
series of flasks was prepared with an average sample of sewage. Zinc 
chloride varying in proportion from 1:500 to 1:40 was added to this 
series of flasks, which were placed at room temperature. A slight 
cloudiness appeared on the tenth day in the flasks of sewage containing 
a percentage of 1:500 of zinc chloride. 
Another series of flasks was prepared by mixing equal quantities b}" 
volume of sewage and tap water. These were also kept at room tem- 
perature, and it was found under these conditions that in the per- 
centage of 1:500 of zinc chloride a bacterial growth developed on 
the fourteenth da}v 
In a third series of flasks containing sewage and nutrient bouillon in 
equal volumes and kept at room temperature as above it was found 
that a bacterial growth developed, indicated b}^ the clouding of the 
bouillon, 'on the fifth day in the flask containing zinc chloride in the 
strength of 1:200, but not in a strength of 1:100 in 14 days. 
The organic matter in the flasks referred to above was soon precipi- 
tated after adding the zinc chloride, and this was particularly the case 
when the zinc chloride was in quantity approximateh’ sufficient to 
inhibit bacterial growth. This precipitate, or residue, was at first 
brownish in color, but soon became more or less bleached. The 
bleaching was more apparent in those flasks receiving sufficient zinc 
chloride to inhibit bacterial development, but was observed to a cer- 
tain extent in all the flasks, the degree of which varied directly with 
the quantity of zinc chloride present. 
After the precipitate in these flasks settled to the bottom the super- 
natant liquid was practically clear and transparent, and when the zinc 
chloride was in quantity sufficient to prevent micro-organic develop- 
ment it gradually assumed a straw color resembling nutrient bouillon. 
Further work was done with these same flasks in order to determine 
