280 The Microscope. 



which there are many superposed, are so thin as to float in air 

 like down when detached. They decompose the light by inter- 

 ference due to reflections from the front and rear surfaces of the 

 film and give rise to the gorgeous play of color for which these 

 ancient specimens of glass are noted. By transmitted light the 

 color is complementary to that shown by reflected light. Ex- 

 amined by polarized light, the color is heightened still moie with 

 all the changes that may be brought about by rotating the polar- 

 izer, analyzer, or the object itself. 



If the effects secured by long ages ol treatment in Nature's 

 laboratory could be produced artificially on modern glass at a 

 reasonable cost, it would seem to be an object well worth striv- 

 ing for, — Prof. George M. Hoi^kins in Scientific American. 



An instrument, called the hdematokrit, has been lately in- 

 vented by Herr von Hedin ; it is for determining the volume of 

 corpuscles present in blood, and is based on centrifugal action. 

 A volume of blood and one of Moller's liquid (which prevents 

 coagulation) are mixed together, and the mixture is brought 

 into small thick-walled glass tubes, graduated in 50 parts. The 

 tubes rest on a brass holder which is fixed on the axis of a rota- 

 tion-apparatus. After some 8,000 rotations, in 5 to 7 minutes, 

 the process is complete. The sepai-ation between the corpuscles 

 and the salt-plasma is more distinct, in that a narrow band of 

 leucocytes appears between them. Tl^e instrument is useful in 

 comparing the blood of different individuals. With a little 

 practice, the total error is not more than one volume percent. — 

 Nature. 



A NEW CULTURE FLUID. — Dr. G. M. Sternberg gives the Medical 

 News a short note, interesting to laboratory workers and others, 

 on the use of the fluid contained in unripe cocoanuts as a culture 

 medium. This fluid, unlike that of the ripe nut, is devoid of all 

 milky appearance and is perfectly transparent. By the people 

 of the West Indies it is known as agua coco, or cocoanut water, 

 and is very popular as a refreshing drink ; at the railway stations 

 and restaurants may be seen piles of the unripe nuts, which at a 

 moment's notice can be broken open and made to yield a tumbler- 

 ful of the fluid at a trifling cost. The cocoanut is a germ-proof 



