116 BACTERIOLOGY. 



PRESERVATION OF BLOOD-SERUM. It is some- 

 times desirable to preserve blood-serum in a fluid 

 state. This can be done by the fractional method 

 of sterilization at low temperatures, already described,, 

 or with much less effort, and without the use of heat, 

 by a method that we have found very satisfactory. In 

 the course of Kirschner's investigations chloroform was 

 shown to possess decided disinfectant properties ; as it is 

 quite volatile, it is easily got rid of when its disinfectant 

 or antiseptic properties are no longer required. If, there- 

 fore, 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 provision is one on which success depends. If 

 the vessel containing 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 chloro- 

 form has been added. When required for use, the 

 serum is decanted into test-tubes, which are then placed 

 in a water-bath at about 50 C. until all the chloro- 

 form 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 em- 

 ployed 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 



