158 STERILIZATION AND DISINFECTION 
We also tried adding 2.5 c.c. of the organic matter to 2.5 c.c. of 
the disinfectant dilution, but found it rather difficult and cumber- 
some to do, particularly when the experiment has to be performed 
with a number of different strengths of the disinfectant. When using 
the proportions as just stated, the dilutions of the disinfectant are 
made double the strengths it is desired to test, thus allowing for the 
further dilution when an equal volume of organic matter is added 
thereto. 
In using the proportions of 1 ¢c.c. of organic matter to 4 ¢.c. of the 
disinfectant dilution we have found the following tables (XIV and XV) 
of service in preparing the dilutions of the disinfectant: 
It will be seen that by preparing the dilutions of the disinfectant 
according to the strengths shown in the second column of Table XIV, 
and then adding 1 c.c. of organic matter to 4 c.c. of the dilutions, the 
final dilutions of the disinfectant become as represented in the first 
columu of the table given above. 
Preparation and Use of the Peptone-gelatine Organic Matter. 
As already stated, we prefer to use a mixture of peptone and gelatine 
dissolve:i in distilled water. It is prepared from Witte’s peptone 
(siccum) and “‘ Best French Gold Label” gelatine. The stock prepara- 
tion is made to contain 10 per cent peptone and 5 per cent gelatine. 
Proportionate amounts of peptone and gelatine, respectively, are 
weighed out and liquefied separately in small quantities of water by 
means of heat. They are then mixed in a graduate and sufficient 
water added thereto to make a mixture containing 10 per cent of pep- 
tone and 5 per cent of gelatine. It is then placed in bottles of appro- 
priate size and sterilized on three successive days. When the mixture 
has become cold it will be observed that some of the peptone settles to 
the bottom of the bottles as a flocculent deposit. Consequently, the 
bottle should be shaken before using it. The stock preparation con- 
taining 5 per cent gelatin becomes semi-solid if it is kept in the cold room: 
at a temperature of 16° C. However, by warming it until it becomes 
perfectly liquefied and then not allowing it to go below the temperature 
of 20° C. we found that it remains liquid and is easily measured in the 
pipette. 
By adding 1 ¢.c. of the stock preparation of 10 per cent peptone 
and 5 per cent gelatin to 4 c.c. of the disinfectant dilutions a result- 
ing mixture is obtained containing 2 per cent of peptone and 1 per cent 
of gelatin, or a total of 3 per cent organic matter. 
The Method of Conducting the Test. Four c.c. of each disinfectant 
dilution, ineluding the phenol controls, are accurately measured into 
