794 



METHODS OF INVESTIGATING BACTERIA. 



Be-inocula- 

 tion. 



25 C., otherwise they will become liquid ; on the other 

 hand, agar mixtures and solidified blood serum may be 

 kept at a temperature of 35 to 39 C. 



The inoculation of these sterilised media must be per- 

 formed with great care ; a small quantity of material 

 containing the organisms is taken by means of a heated 

 platinum wire, or of a fine glass tube, and the cotton 

 wool plug being removed for the moment the wire is 

 introduced into the nutrient material. In this method 

 the entrance of organisms from the air is never quite 

 excluded, but as the danger of contamination from the 

 air is much less than from the instruments employed, 

 this source of error is not of any great importance in 

 practice. However, it is advisable in all cases where we 

 wish to be certain as to the purity of the cultivations, to 

 avoid draughts in the room, shaking of the room, &c., 

 and if necessary to moisten the floor and the walls. It 

 is well for the experimenter to wash his hands in sub- 

 limate solution before proceeding to the inoculation. 



Some 



Special Methods of Cultivation. 



cial Small cultivations, such as those on hollow micro- 

 scopic slides, or in the so-called " glass chambers," are 



Fig 1 . 141. Drop cultivations. 

 , the hanging drop. b, the layer of vaseline. 



of use for studying the stages of development of a species 

 Drop cultiva- of bacteria which has already been cultivated pure. The 

 most simple mode of carrying on these cultivations is by 



tions. 



