114 
PROFESSOR P. F. FRANKLAND AND MRS. O. C. FRANKLA.ND ON 
Dilution Experiments, Series I., commenced October 20 , 1887. 
50 c.c. of sterilised distilled water were placed in a sterile stoppered bottle and then 
inoculated with a few drops taken from the “ sixth generation ” (see p. 11 3), and the 
mixture was then violently shaken for some time to thoroughly disintegrate any 
coherent masses of oi’ganisras that might have been introduced. From the attenua¬ 
tion thus prepared a number of test-tubes containing sterile ammoniacal solution were 
respectively inocidated with one loop of a platinum needle, another series of test-tubes 
with two loops, and a single test-tube received as much as twelve drops from the 
above attenuation. 
The several tubes thus inoculated on October 20, 1887, were examined on November 
30, 1887, when the one which had received twelve drops yielded strong reactions both 
with diphenylamine and sulphanilic acid, whilst the tubes inoculated with one and 
two loops respectively gave no reactions, nor did they when subsequently examined on 
December 23, 1887. Thus only in the case of the tube which had received twelve 
drops had auy nitrifying organisms been introduced, whilst the smaller quantities 
(one and two loops) employed for the other tubes must have been quite free from 
these organisms. 
The solution which had been nitrified with the twelve drops added as above was 
reasonably to be regarded as purer than the “ sixth generation ” from which it had 
been obtained by large dilution. This “ twelve-drop attenuation ” as it may be called, 
therefore, was cultivated further in successive generations, each giving rise to well- 
marked nitrification. The third generation of this series was plate-cultivated, and 
inoculations made with a number of the colonies, but in no case did nitrification result. 
The second generation of this twelve-drop attenuation was employed as the starting 
point for the 
Dilution Experiments, Series II., commenced March 5, 1888. 
The solution used for dilution in these experiments had been inoculated on 
December 1, 1887, it was found to have nitrified on December 23, 1887, but on 
re-examining on March 5, 1888, it not only gave reactions with diphenylamine and 
sulphanilic acid, but also with Nessler’s solution, and it might, therefore, be taken 
that the nitrifying organism was still in fall activity. Two drops of this solution 
were added to about 50 c.c. of sterilised water, well shaken, and then five bottles con¬ 
taining sterile ammoniacal solution were inoculated as follows : — 
No. 1 bottle with 9 drops. 
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