102 BACTERIOLOGY. 



pipette in the hand and sucking upon the rubber tube 

 one can more easily direct the point of the pipette than 

 if it is used in the ordinary way. 



The bulbs are easily blown, and after having been 

 sealed at the point and plugged with cotton can be kept 

 on hand just as are sterilized test-tubes. 



It is sometimes 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 to be very satisfactory. 

 In the studies of Kirchner chloroform was shown to 

 possess decided disinfectant properties; as it is quite 

 volatile, it is easily removed when its disinfectant or 

 antiseptic functions 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. 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 chloroform has been driven off; this can 

 be determined by the disappearance 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. 



SPECIAL MEDIA. The media just described bou- 

 illon, nutrient gelatin, nutrient agar-agar, potato, and 

 blood-serum are those in general use in the laboratory 

 for purposes of isolation and study of the ordinary 

 forms of bacteria. For the finer points of differentia- 



