154 Methods of Observing Bacteria 



water, then with absolute alcohol, then again with distilled 

 water. All three washings must be very thorough. 



2. Bain sensibilisateur: 



5 per cent, solution of nitrate of silver in distilled water. 



The films are allowed to remain in this for a few seconds, 

 and are then immediately transferred to the third bath. 



3. Bain reducteur et reinforfateur: 



Gallic acid 5 grams 



Tannin 3 



Fused potassium acetate 10 



Distilled water 350 c.c. 



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 modifies the method by allowing the 

 preparations to remain in the second bath for two minutes, 

 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. 



Measurement of Bacteria. Bacteria can best be 

 measured by an eyepiece micrometer. As these instruments 

 vary somewhat in construction, the unit of measurement 

 for each objective magnification and the method of manipu- 

 lating the instruments must be learned from dealers' cata- 

 logues. 



Photographing Bacteria. Photographing bacteria re- 

 quires special apparatus and methods. For a sufficient 

 description of the necessary technic it is necessary to refer 

 to special text-books upon the subject.* 



* See the excellent chapter upon Photomicrography in Aschoff and 

 Gaylord's "Pathological Histology." Philadelphia, 1900. 



