1891.] MICKOSCOPICAL JOURNAL. 237 



an arranged slide of diatoms prepared by Rinnbcick, of Vienna. 

 Cliarles C. Riedy exhibited a Navicula lyra with a one-fourth inch 

 apochromatic objective and dark field. 



R. H. Freund showed the only preparation of bacteria on exhibition, 

 a species of pathogenic bacteria not identified. E. S. Runyon had a 

 number of very attractive crystals, including the crystalizable principle 

 from the prickly pear. Platino-cyanide of magnesium and Menthon 

 crystals, all shown with polarized light and excellent effect. William 

 E. Loy showed a young star-fish, Asterium gibbosa^ with the aid of 

 a spot lens. 



The exhibition was further enhanced by brief informal addresses. 

 Mr. Hyde gave an outline history of the Dlatomacce^ showing first 

 their place in botany, how generally they are dispersed about the globe, 

 where they may be found, and a comparison of the fossil and recent 

 forms. The peculiar structure of the diatom has preserved very perfect 

 skeletons from the earliest geologic eras in which it is found, and when 

 properly treated these fossils may be cleaned and mounted, yielding the 

 most beautiful of all microscopic objects. He remarked that since the 

 time of Ehrenberg many scientists had spent years of patient study in 

 this captivating field, so that to-day many thousand species had been 

 figured and described. Unlike some objects in nature, new beauties 

 are seen with increased amplification, and the highest powers of the 

 microscope only serve to increase the admiration of the beholder. 



A. H. Breckenfeld gave a brief demonstration of the optical qualities 

 of what is known as dark field illumination. By this method the light 

 is thrown around and upon the object, but its rays do not enter the ob- 

 jective nor reach the eye of the observer. The object then is shown on 

 a dark background, with a brilliancy not possible where the light 

 passes directly through the object. His remarks were fully illustrated 

 by drawings on the black-board, and proved instructive and interesting. 



Septeniber 2, i8gi. — Vice-President Selfridge in the chair. The 

 Secretary reported a donation of two pamphlets to the library, from 

 the author, " The Structure of Blood Corpuscles and Its Relation to 

 Practical Medicine," and " Fugitive Blood Corpuscles in a case of 

 Lymphadenoma," by J. H. Wythe, M. D., LL.D. ; two parts of 

 " Bolletino della Societa Italiana dei Microscopisti," from the sister 

 society in Acireale, Italy ; besides the usual installment of periodicals 

 and journals for the reading table. 



The routine business of the evening included the election of H. M. 

 Miner, M. D., as a regular member. 



The paper announced for the evening was read by Dr. Wythe, on 

 " The Structure of Blood Corpuscles." After mentioning his studies 

 and researches in this branch of histology and certain recorded results, 

 he stated that these observations extended over a number of years and 

 had been prosecuted with the highest powers of the microscope, es- 

 pecially with the Leitz one-twelfth and one-twentieth homogeneous im- 

 mersion glasses, and the Bausch and Lomb one-eighth of i .43 numerical 

 aperture. « 



Since then he has received a Powell and Leland one-tenth apochro- 

 matic homogeneous immersion objective, of the extreme numerical 

 aperture of 1.50, and last evening he exhibited the blood corpuscles 

 under that magnificent lens. He said that preliminary to the demon- 



