THE PREPARATION OF CULTURE MEDIA 33 



well for sucli manipulations. Care must be taken that 

 the wire is permitted to cool before use, and during the 

 minute which elapses in so doing nothing must be 

 allowed to come in contact with it. It is often quite 

 sufficient to simply use a straight piece of platinum 

 wire instead of bending it into a loop, as in the majority 

 of cases enough material can be conveyed even on the 

 point of such a platinum needle. 



Having obtained some of the material, we take a 

 melted gelatine-tube, observing in opening it all the 

 precautions previously described, and insert the infected 

 needle into the gelatine, the needle is then rapidly with- 

 drawn and the cotton-wool stopper replaced. The 

 needle should be immediately sterilised ; this is of course 

 especially necessary in working with pathogenic micro- 

 organisms. 



The gelatine-tube thus infected must be carefully 

 shaken to ensure the distribution of the micro-organ- 

 isms throughout the mass of the liquid gelatine ; if 

 we were immediately to pour a plate with this we 

 should in all probability obtain such an enormous 

 number of colonies and so densely crowded together 

 as to prevent their proper individual development. To 

 obviate this we take another gelatine-tube and transfer 

 from the original tube, or first attenuation as it is gene- 

 rally called, one loop to this second tube, and, after 

 thoroughly mixing, several loops from this second tube 

 to a third. It is essential that in each case the gelatine 

 should be gently but thoroughly shaken, so as to ensure 

 the even distribution of the individual organisms which 

 have been introduced. The amount transferred from 

 one tube to another must be varied according to the 

 judgment of the operator, and after a little practice 

 there is generally little difficulty in procuring success- 

 ful attenuations or plates in which the colonies are so 



D 



