MILK 125 



its disinfectant or antiseptic properties are no longer required. 

 If, therefore, the serum to be preserved be placed in a closely 

 stoppered flask and enough chloroform added to form a 

 thin layer, about 2 mm., on the bottom, the serum may 

 be kept indefinitely without contamination, so long as the 

 chloroform is not permitted to evaporate. This latter pro- 

 vision is one on which success depends. If the vessel con- 

 taining the mixture of chloroform and serum be not tightly 

 corked, the chloroform vapor escapes pretty rapidly and 

 exerts no preservative action. In fact, bacteria will grow 

 uninterruptedly in a cotton-stoppered test-tube containing 

 bouillon to which chloroform has been added. When re- 

 quired for use, the serum is decanted into test-tubes, which 

 are then placed in a water-bath at about 50 C. until all 

 the chloroform has been driven off; this can be determined 

 by the absence of its characteristic odor. The serum may 

 then be solidified, sterilized by heat, and employed for 

 culture purposes. We have found serum so preserved to 

 answer all requirements as a culture-medium. 



MILK. 



Fresh milk should be allowed to stand over night in "an 

 ice-chest, the cream then removed, and the remainder of 

 the milk pipetted into test-tubes, about 8 c.c. to each tube, 

 and sterilized by the intermittent process, at the tem- 

 perature of steam, for three successive days. 



The separation of the cream may be accelerated and 

 rendered more complete if the cylinder containing the milk 

 be placed in the steam sterilizer for fifteen minutes before it 

 is placed in the ice-chest. 



The cream is best separated from the milk by the use of 



