22 
EFFECTS OF ZINC CHLORIDE UPON SPORE-BEARING ORGANISMS. 
Experiments were performed with T-days-old agar cultures of B. 
subtilis and B, antJiracis. A banging-drop preparation of each cul- 
ture was examined before it was used to see that it contained many 
spores. 
Preparations of zinc chloride varying from 5 to 100 per cent were 
prepared in distilled water and 20 c. c. of each strength placed in a 
large test tube. It may be well to state here that by a 100 per cent 
solution of zinc chloride is meant a solution made by adding enough 
distilled water to a given number of grams of diw zinc chloride to 
make the same number of cubic centimeters of solution. The dilu- 
tions were made accordingly. For the purpose of exposing the 
spores in these solutions of zinc chloride different methods w^ere 
emplo}’ed. In some experiments a wntery suspension of the organ- 
isms to be used was made and added to the different solutions of zinc 
chloride, after which plants from each tube into nutrient bouillon 
were made at deffnite intervals and placed in the incubator at 37^ C. 
The results show that the spores of B. subtilis w'ere still viable 
after 1 days’ exposure in a 100 per cent solution of zinc chloride, but 
produced no grow^th when transplanted after 5 days' exposure in the 
same strength. The spores of B. antJiracis were capable of multi” 
plying when transplanted into bouillon after an exposure of 7 days in 
a 2.5 per cent solution of zinc chloride. 
An objection to the above mode of procedure is that when the 
inoculated solutions of zinc chloride are to be kept for a long period, 
say a month, some of the organisms that adhere to the sides of the 
test tube above the liquid, and consequently are not immersed in it, 
are liable to be carried over in making the plants from time to time 
and give erroneous results as to the germicidal value of the substance 
being determined or the viability of the organism under test. 
This is more likely to occur if the contents of the tube are shaken 
up before making the inoculations. 
By using a sterile pipette for making the inoculations and carefully 
carrying it to the bottom of the tube, as was done in the above experi- 
ments, this possible source of error is reduced to a minimum. The 
principal objection to the use of the pipette for this purpose is that 
too much of the zinc-chloride solution is carried over. 
The silk-thread method wns also used for exposing the organisms in 
the zinc-chloride solutions and proved more satisfactory than the 
preceding method. Sterile silk threads about 1 inch long were soaked 
in a thick watery suspension of the organism to be used and about 20 
threads placed in each strength of zinc chloride. Inoculations were 
made at deffnite intervals by carefullv transferring a thread to nutrient 
bouillon and placing in the incubator at 37^ C 
