118 THE AMERICAN MONTHLY [April 



cyanide aud the plate must be carefully watched during 

 the process that the reduction may not he carried too far. 

 By reduction, or intensification, or by employiug- both 

 one after the other, a negative may sometimes be obtained 

 from an o])ject so diflBcult that the simple [)rocess of ex- 

 posure and development will not suffice. But these pro- 

 cesses should only be resorted to when strictly indicated 

 and after different lengths of exposure and careful adjust- 

 ment of the substage illumination have failed to give the 

 required result. 



In photomicrography, arrangement of the light and 

 adjustment of the substage condensers are of primary 

 importance and unless the details of their arrangement 

 are mastered, no attention to development, or subsequent 

 doctoring of the negatives, will give good results. But 

 with these understood, the limit of their effectiveness will 

 be known and when this is reached, the chemistry of the 

 photographic process may be resorted to with profit. 



The Practical Results of Bacteriological Kesearches. 



BY GEORGE M. STERNBERG, M. D., LL. D., 

 SURGEON GENERAL, U. S. A. 



Gentlemen: In selecting a subject for my j'resi'idential 

 address I have thought it best to restrict myself to that 

 branch of biological science with which I am most 

 familiar; and, as a technical paper might prove uninter- 

 esting to many of those who constitute my present 

 audience, I have chosen a title for my address which will 

 enable me to speak in a general way of the development 

 of our knowledge relating to the low vegetable organ- 

 isms known as bacteria, and the practical results which 

 have been the outcome of researches commenced in the 

 first iustynce solely on account of their scientific interest. 



Attention was first prominently called to the bacteria 



