54 



THE AMERICAN MONTHLY 



[March 



and solutions of gold and silver salts 

 were also tried with negative results. 

 Finally the cell-wall of the bacteria 

 was subjected to a photo-chemical 

 process in the following manner : 

 After the drop containing the bacteria 

 is dried upon the slide in the usual 

 manner, the spot is moistened with 

 an aqueous solution of a metallic 

 iodide (cadmium iodide i : 50 was 

 employed ) and in two or three 

 minutes the bacteria are sufificiently 

 iodized. The slide is then carefully 

 and rapidly washed with distilled 

 water, and immediately flowed with a 

 few drops of silver-solution from the 

 negative-bath. If the process has 

 been properly conducted, if the iodide 

 has acted long enough and the 

 subsequent washing has not been 

 continued too long, the contour of 

 the dried spot will be seen to show 

 a yellow color, due to iodide of silver 

 which is formed. A momentary ex- 

 posure to light is sufficient, after 

 which the developer ( strongly aci- 

 dified and dilute iron-developer) 

 is added, and the drop suddenly 

 becomes black. After thorough wash- 

 ing, the deeply colored bacteria are 

 mounted in balsam and they may 

 then be readily photographed. Even 

 the Bacterium termo is thus readily 

 pictured. 



This method is only useful for 

 photographic purposes, and there is 

 some chance of mistaking fine silver 

 precipitates for micrococcus or other 

 forms. In case of any doubt of this 

 kind, the original forms should be 

 stained with anilin colors and ex- 

 amined in the usual way. 



EDITORIAL. 



— This number of the Journal 

 will be sent to many who are not 

 subscribers, in the hope of inducing 

 them to send in their names, and one 

 dollar for the current volume. 



Every new subscriber contributes 

 just so much, not only to the support 

 of the Journal, but also toward its 



excellence and value, by enabling tht 

 publisher to spend more money foi 

 the illustration of valuable articles 

 We solicit the support of every mar 

 who is a member of a microscopica 

 society. If we could obtain this, wt 

 would ask for nothing more. 



Physics of the Microscope. — So 

 many correspondents have expressed 

 a desire to have us publish some 

 articles upon this subject, that we 

 have finally concluded to print the 

 greater part of an article which we 

 read about a year ago before the N. 

 Y. Academy of Sciences. It has been 

 our intention to write some articles 

 for the Journal upon this subject, 

 but upon looking over the one already 

 written it seems to cover the ground 

 very v/ell. 



o 



Catalogue of Diatomace^. — 

 We are pleased to announce that the 

 publication of this valuable catalogue 

 of Mr. F. Habirshaw, is now assured. 

 The subscriptions are barely suffi- 

 cient to pay for the cost of the print- 

 ing, but the work was not undertaken 

 in the expectation that it would 

 prove remunerative. The manu- 

 script will soon be in the printer's 

 hands, and the first part will probably 

 be ready for distribution in the course 

 of two months. 



Handbook of Adulterations. — 

 In consequence of the demands upon 

 our time, which the immediate publi- 

 cation of Mr. Habirshaw's " Cata- 

 logue " as well as other work of a 

 different nature necessitates, we have 

 decided to withdraw the " Handbook 

 of Adulterations " for the present. 

 Numerous contributions have lately 

 been made to the subject of adultera- 

 tion, and the delay will enable us to 

 make the work still more valuable. 



Fresh-Water Rhizopods. — The 

 valuable work by Prof. Joseph Leidy, 

 on the " Fresh-water Rhizopods of 

 North America," has received well- 



