34 



THE WEST-AMEBICAN SCIENTIST. 



SOCIETIES. 



The regular semi-monthly meet- 

 ing of the San Francisco Micro- 

 scopical Society, was held at the 

 Society's rooms, No. 120 Sutter 

 St., on Wednesday evening, March 

 11, 1885. Sundry scientific peri- 

 odicals were added to the files. 



Dr. Selfridge exhibited an in- 

 teresting specimen of supposed 

 meteoric origin. Its surface and 

 outlines were more regular than 

 is usually the case with meteor- 

 ites, but it possessed one charac- 

 teristic of those interesting bod- 

 ies in a remarkable degree, viz: 

 extreme hardness . 



Dr. S. M. Mouser then exhibi- 

 ted his newly acquired microtome 

 or Section Cutter, of the celebra- 

 ted "Thoma" pattern. It is ex- 

 ceedingly elaborate in construc- 

 tion, but consists essentially of a 

 frame of cast iron, on which slide 

 two carriers. A large and finely 

 finished knife is clamped to one 

 of these, which slides on a hori- 

 zontal plane. The second carrier 

 ( which holds the specimen to be 

 cut) moves on an inclined surf ace. 



Professor Thorn x has based the 

 construction of this microtome 

 upon the principle (first theoreti- 

 cally deduced, and than practi- 

 cally demonstrated) that a body 

 sliding between two inclined 

 planes and touching the latter at 

 five points only, will slide evenly 

 and exactly over such planes even 

 if they be not geometrically true. 

 A knife attached to such a carrier 

 will, therefore, always cut per- 

 fectly parallel sections of an ob- 

 ject which is elevated after each 

 eat. As a practical exemplifica- 

 tion of the perfection with which 



the above principle has been work- 

 ed out in the Thoma microtome, 

 it may be stated that it permits 

 the cutting of serial sections of 

 well hardened animal tissues of 

 certain kinds, as thin as .002 mm. 

 (.00008 in.), and even such a com- 

 paratively coarse tissue as liver 

 can, if well hardened, be cut to 

 .01 mm. (.0004 in.) The ability 

 to produce sections of such won- 

 derful delicacy has given a great 

 impetus to histological and patho- 

 logical research of late. 



Mr. Breckenfeld exhibited a 

 "Graduated Blue Glass Modifier" 

 which has just been brought out 

 by the Bausch and Lomb Optical 

 Company. 



At the meeting of March 25, 

 1885, a valuable donation was re- 

 ceived from Lieutenant Thos. L. 

 Casey, U. S. A., consisting of 

 three volumes of his "Contribu- 

 tions to Coleopterology," just pub- 

 lished. 



D. J. N. Stallard of this city 

 was nominated for resident mem- 

 bership. 



On the announcement that a 

 new and much enlarged edition 

 of Habirsliaw's rare and valuable 

 "Catalogue of the Diatomaceae" 

 was about to be published, it was 

 unanimously resolved to order a 

 copy for the Society's library. 



A very interesting demonstra- 

 tion of the capabilities of a new 

 opthalmoscope was given by its 

 inventor, Mr. Louis A. Berteling. 



He also exhibited the "Profes- 

 sional" microscope, manufactured 

 by the Bausch & Lomb Optical 

 Co., and being the most elaborate 

 form made by it. Nearly all the 

 revolving parts are furnished with 



