1890.] MICROSCOPICAL JOURNAL. 143 



San Francisco, Cal. — Wm. E. Loy, Sec'y. 



Wednesday^ April 23^ i8go. — A number of accessions to the library 

 were reported, including the "Journal of the Liverpool Microscopical 

 Society." A communication from Professor Hanks was read, which 

 stated that on the 4th of June, 1870, the San Francisco Microscopical 

 Society was organized. It was deemed advisable to make the 20th 

 anniversary one of special interest, and the President appointed a Com- 

 mittee of Arrangements. 



A communication on the subject of a new flash-light for photograph- 

 ing was read by the Secretary. This was a memorandum from the pro- 

 ceedings of the Washington Chemical Society before which Dr. Thomas 

 Taylor, of the Department of Agriculture, made the exhibition of his 

 new discovery, which, it is believed, will supersede several now in use 

 for photographing at night. The composition consists largely of char- 

 coal made from the silky down of the milk weed — a form of carbon 

 which he prefers to all others, because of its freedom from ash. A few 

 grains being placed on tissue paper and ignited by a punk match, pro- 

 duced a prompt and blinding flash, while it was observed tliat the 

 paper on which the powder rested was not even scorched, thus demon- 

 strating the greater security from accidents. Mr. Breckenfeld thought 

 it probable that this new discovery would prove of value in photograph- 

 ing infusoria and other living minute organisms with the aid of the 

 microscope. 



The event of the evening was the exhibition of a splendid series of 

 photo-micrographs and appropriate remarks by E. W. Runyon. The 

 speaker described his method of procedure in detail, and to further 

 illustrate his topic had his apparatus on exhibition. For the purpose 

 he used his Bulloch stand, the tube in a horizontal position, the eye- 

 piece entering a camera made especially for the purpose. The tube 

 should be lined with velvet, or blackened, and in focussing a hand-mag- 

 nifying glass was used behind the ground glass, to secure sharp defini- 

 tion. All the photo-micrographs exhibited by Mr. Runyon were made 

 at night with oil light. 



The addition to a sensitive film of certain coloring matters, which are 

 known as optical sensitizers or selective sensitizers, renders the film 

 sensitive to rays which would otherwise produce little or no photo- 

 graphic effect. This discovery was made by Vogel in 1S73. The ra3^s 

 to which the film is thus made sensitive are rays which it would not 

 absorb under ordinary conditions, but which it can absorb after treat- 

 ment with the dye. The dyes used are of the eosin group. Eosin 

 sensitizes for green and yellowish green, and erythrosin for yellowish 

 green and greenish yellow. For photographing many microscopic 

 preparations, such as stained sections of animal and vegetable tissues, 

 the orthochromatic plates had given excellent results. 



With a 3-inch objective, the exposure, even with the light of a stu- 

 dent lamp only, should be very brief — practically instantaneous ; with 

 a \ or 1-inch objective, a longer exposure must be had, the duration of 

 which would depend largely on the nature of the object to be photo- 

 graphed. Particular attention was directed to the photo-micrograph 

 of a vertical section of the human scalp, showing with great clearness 

 the hair follicles, fat cells, glands, etc. ; and as examples of fine details 

 the head of horse-fly, proboscis of blow-fly, and arranged diatoms. 



