234 



THE AMERICAN MONTHLY 



[December, 



chccolate, and not flavored. It may 

 be a really good preparation, well 

 worth its price, or a very inferior 

 article owing to the quantity of starch 

 it contains. If we once understand 

 that cocoa can be prepared without 

 starch the microscopist will be able to 

 select the pure siDCcimens at a glance. 

 As regards the chocolates the task is 

 not so eas}^, but experience will lead 

 to useful results by microscopical ex- 

 aminations far more quickly than by 

 chemical analysis. The true value of 

 a chocolate will depend not absolutely 

 ujjon the proportion of starch and 

 pure cocoa which it contains, but also 

 upon the amount of fatty matter. The 

 fatty matter of the bean necessitates 

 the addition of starch in the prepara- 

 tion of chocolate, but the addition of 

 more starch than the quantity of fat 

 present in any preparation requires, 

 constitutes an adulteration. 



New Slides of Diatoms. 



[Mr. C. L. Peticolas has sent us 

 the following communication relating 

 to some very beautiful slides he has 

 recently prepared. — Ed.] 



Slide No. \. — Stauronds acuta. 

 Microscopists are familiar with the 

 beautiful effects of dark-field illumi- 

 nation upon certain diatoms. Some 

 peculiarities of structure are shown by 

 this method more clearly than by 

 transmitted light. A recent gathering 

 of St. acuta-Flcurostaui-um aciituum, 

 Grunow, has given me a sensation, 

 although I have practiced this method 

 of illumination for years. With a ^- 

 inch objective and strong artificial 

 light on dark-field, this diatom seems 

 literally to blaze, and surpasses in 

 splendor the finest polariscope objects 

 in my cabinet. With the light thrown 

 across the short diameter, there is 

 strong resemblance to a section of 

 ostrich tendon, only some peculiarity 

 of striation seems to impart motion to 

 the light, and the diatom seems on 

 fire ; across the long diameter the 

 color is changed to a brilliant 

 sapphire. 



Slide No. 2 contains a recent gath- 

 ering from Fernandina, Fla., which 

 gives the best showing of the beauti- 

 ful marine diatoms of that coast, I 

 have yet seen. I have noted the 

 following forms, among others, and as 

 there is quite a number not yet 

 identified, and the forms are shown 

 generally in perfection, it will be seen 

 that this is an exceedinglv interesting 

 deposit : — 



Eupodiscus argus, radiatus ; Tricera- 

 tiiim favus., pjok-tatum, spi?iosum, 

 (rare) ; Naviada lyra (several vari- 

 ties), Formosa ; Pleiirosigma Balticum, 

 angulatum (rare) : delicatulum (rare) ; 

 Actinocycliis, Ehr. ; Biddulphia rhom- 

 bus, puliheila, and other species ; 

 Terpsinoe musica, Americana; Amphi- 

 prora elcgans, pulchra (rare) ; Coscino- 

 discus excentricus, radiatus (?) ; Surri- 

 rella three species; Raphomis rhombus ; 

 Fragillaria Schivarzii (rare) ; Stauro- 

 neis aspera ; Nitzschia five species; 

 Orthosira marina ; Triceratiujn, three 

 species ; Actinoptychus undulatus, 

 splcndens ; Auliscus sculpt us, pruino- 

 sus ; Biddcilphia rhombus, tuomeii ; Coc- 

 concis Pacijica ; Campy Iodise us echineis, 

 imperialis ; Podosira maculata ; Scoli- 

 opleura tur?}iida, late striata. 



A New Moimting Fluid. 



G. W. MOREHOUSE. 



For preserving the cell-contents 

 and he natural color and form of 

 desmids, volvox, and other algas, I 

 find a mounting fluid made as follows 

 to act well : Dissolve 15 grains of 

 acetate of copper in a mixture of 4 

 fluid ounces of camphor water, 4 fluid 

 ounces of distilled water, and 20 

 minims of glacial acetic acid ; add 8 

 fluid ounces of Price's glycerin, and 

 filter. 



When sections of plant-stems, or 

 other vegetable specimens, are mount- 

 ed in this fluid, the protoplasm is 

 preserved. If, in any case, it is 

 thought desirable to increase or 

 diminish the specific gravity of the 

 preservative, the proportion of glyce- 



