l62 PATHOGENIC BACTERIA. 



The preparations are kept in this solution for a few 

 seconds, then returned to the nitrate of silver solution 

 until they begin to turn black. They are then washed, 

 dried, and mounted. 



Mervyn Gorden recommends that the method be modi- 

 fied by allowing the preparations to remain in the second 

 bath for two minutes, then transferring to the third bath 

 for one and a half to two minutes, and then washing, 

 drying, and mounting without returning to the second 

 bath. 



Muir and Ritchie find it advantageous to use a fresh 

 supply of the third solution for each specimen. 



Bacteria can best be measured by an eye-piece microm- 

 eter. As these instruments vary somewhat in con- 

 struction, the unit of measurement for each objective 

 magnification or the method of manipulating the adjusta- 

 ble instruments must be learned from dealers' catalogues. 



Photographing bacteria requires special apparatus and 

 methods, which are fully described in text-books upon 

 the subject. 



