178 



THE AMERICAN MONTHLY 



[September, 



to indicate microscopical dimensions, 

 should be accurately ascertained, carfe 

 being taken that the minuteness of 

 dimensions and genei'al delicacy and 

 perfection of the test-object should be 

 adapted to the power of the lens. A 

 fairly correct estimate of the relative 

 performance of lenses of moderate 

 magnifying power may, doubtless, be 

 thus made by a competent observer, 

 but it is not possible from any com- 

 parisons of this kind to determine v^^hat 

 may or ought to be the ultimate limit 

 of optical performance, or whether 

 any particular lens under examination 

 has actually reached this limit. 



' Assuming the manipulation of the 

 object to be as perfect as possible, 

 and, further, that the test-object has 

 been selected with due appreciation 

 of the I'equirements of perfect optical 

 delineation, a fair comparison can 

 only be drawn between objectives of 

 the same magnifying power and aper- 

 tiu'e. Which of two or more objec- 

 tives gives the better image may be 

 readily enoiigh ascertained by such 

 comparison, but the values thus ascer- 

 tained hold good only for the particu- 

 lar class of objects examined.' 



NOTES. 



— After an experience of three years 

 with balsam of tolu as a mounting medi- 

 uni, M. G. Amann recommends it for the 

 mounting of diatoms in preference to 

 Canada balsam. In the Bulletin of the 

 Belgium Microscopical Society he says : — 

 ' It has given me excellent results, and 

 comparative trials have shown that its 

 optical properties are at least equal to 

 those of storax. Moreover, its prepara- 

 tion is simpler ; it suffices to discolor one 

 part of balsam in two or three parts of 

 chloroform, and filter the solution.' It is 

 more deeply colored at first than storax, 

 but becomes decolorized with time, espe- 

 cially if exposed to light. 



— According to experiments by Prof. J. 

 Richard, published in Zoologischer An- 

 zeiger, the chlorhydrate of cocaine prom- 

 ises to be a valuable reagent for.killing cer- 

 tain organisms, such as bryozoa, worms, 

 and hydras. A small colony of bryozoa 

 is placed in a watch-glass with 5 c. c. of 



water. When fully extended, about half 

 a cubic centimetre of solution of cocaine 

 to each cubic centimetre of water is added, 

 little by little. After five minutes these 

 animals, which, under ordinary condi- 

 tions, retract their tentacles on the least 

 agitation of the water, remain extended in 

 spite of violent shocks. Another Yz c. c. 

 of cocaine solution is now added, and after 

 ten minutes the animals are dead and fully 

 expanded. This reagent should be tried 

 on other animals, and the results recorded, 

 as the author believes its application may 

 be greatly extended. 



— A very interesting experiment, show- 

 ing the influence of light uport the forma- 

 tion of starch in leaves, can be readily 

 performed according to a method recently 

 described by Sachs. To show the starch 

 grains a leaf must be bleached and made 

 transparent in this way : The fresh leaf is 

 placed in boiling water for ten minutes, 

 after which the chlorophyll is extracted by 

 placing it in alcohol. The color is thus 

 removed without rupturing the cells, which 

 retain the starch. The latter is then made 

 visible by treatment with iodine. The 

 cellular tissue becomes stained dark blue 

 or lighter, according to the quantity of 

 starch present. 



Comparative experiments may be made 

 by exposing half of a leaf to sunshine 

 while the other half is protected. A leaf 

 collected in the evening contains much 

 more starch than in the morning. 



— The Association of the Alumni of the 

 Albany Medical College have published 

 the proceedings of their twelfth annual 

 meeting in a pamphlet of 68 pages. It 

 contains an address by Horace T. Hanks, 

 M. D., president of the association, and 

 two lectures by William H. Thomson, M. 

 D., on the germ theory of disease. 



— To color brass diaphragms or other 

 articles black or steel-grey, the Brit. 

 JoMrn. Phot, says, take a quarter of an 

 ounce of sulphate of copper and half its 

 weight of hyposulphite of soda, and dis- 

 solve them in a little more than a pint of 

 water. Thoroughly clean the article, place 

 it in the solution and heat it. More hypo- 

 sulphite will give a darker tint, more sul- 

 phate of copper a lighter steel-grey color. 



— Several years ago an English gentle- 

 man, Mr. Charles Blackley, attempted to 

 determine the number of grains of pollen 

 floating in the air, and also their distribu- 

 tion. He collected them upon squares of 

 glass coated with a sticky medium and 

 counted the number of grains found. In 

 some experiments the squares were sent 



