TEXT-BOOK OF BACTERIOLOGY. 107 



ing colonies in particular soon spoil the solid culture medium. 

 Foreign organisms, especially mould fungi, soon show themselves 

 on the surface, and it is therefore desira"ble to place in safety such 

 bacteria as we particularly^ want without delay. 



This is done by removing the colony in question with the plati- 

 num needle, and transplanting it into a test-tube containing solid 

 gelatin, agar, etc. ; here it can develop quietly and continue the pure 

 culture. Certain precautions must, however, be adopted. Above 

 all, this rule must be followed : never remove a colony from the 

 plate without the direct aid of the microscope. 



The distinguishing peculiarities of these smallest pure cultures 

 are not clearly seen till the microscope is brought into requisition. 

 Besides this, we can never know by the unassisted eye whether we 

 have on our needle only one colony which we wish to transplant 

 or whether we have at the same time touched a number of others. 

 The colonies sometimes lie so closely together in the mass of the 

 gelatin that a mistake may easily happen, and the greatest caution 

 is necessary. 



There is a certain definite series of manipulations which has 

 been found in practice to be the best means of " fishing " for col- 

 onies. 



We first seek a colony suitable to be transplanted — of course 

 using a low power objective, strong eye-piece, and the smallest 

 diaphragm aperture. If we have the choice of several colonies of 

 the same species, we should give the preference to such as are most 

 isolated, have already attained a certain size, and reached the sur- 

 face of the gelatin. The last point in particular very greatly facil- 

 itates the operation of fishing. 



Then bring a short, not too thick, previougly-heated platinum 

 wire close under the lens, and endeavor to get the end of it just 

 over the centre of the colony. This is the most difficult part of the 

 whole operation. The best way of proceeding is to lay the lower 

 half of the little linger of the right hand on the stage of the micro- 

 scope, then hold the wire, as horizontally as possible, close under 

 the objective. When this is done, look through the microscope and 

 the wire will be seen, especially if it be moved slightly backward 

 and forward, as a faint shadow. The more it is lowered the more 

 distinctly it becomes visible. Direct its point into the centre of the 

 field, and dip it into the colony by a slight movement of the hand, 

 which still rests on the stage. It is then at once raised, and the 

 colony generally bears plain marks of the violence done to it. 



It is self-evident that a wide interval between objective and ob- 

 ject is here desirable, that we may have the necessary room for 



