224 SUMMARY OF CURRENT RESEARCHES RELATING TO 



this being done at least ten times if the gelatin is a very poor sample. 

 Finally, the gelatin should be melted by the aid of heat, and purified 

 by the addition of egg-albumen. The whites of two eggs should be 

 allowed for every pound of dry gelatin, and they should be beaten up 

 to a froth, allowed to again become liquid, and then filtered and added 

 to the cool liquid gelatin. Enough glacial acetic acid should be added 

 to give the mixture a distinct acid reaction. The liquid should now be 

 quickly heated to 212° F. and well stirred, when the whole of the albu- 

 men will be coagulated, and can be easily filtered out, carrying with it 

 any solid impurities in the gelatin. The result is a perfectly clear limpid 

 gelatin, which may be used as usual. 



Note on Stereo-photomicrography.* — A. E. Smith describes three 

 ways of making stereoscopic slides from microscopic objects. 



1. The simplest way is to use an excentric Waterhouse stop just 

 behind the objective. After taking a negative the stop is reversed, and 

 another negative taken. The prints from these negatives are distinctly 

 different, and will make good stereoscopic pairs. The author explains 

 many of the practical details. 



2. Another method, suitable for low powers only, is to tilt the object 

 first one way and then the other, and secure a negative in each position. 



3. The object may be moved a short distance across the stage, and 

 a negative secured at either end of the movement. This necessitates 

 the use of a larger camera, as the images do not come exactly in the 

 same place. 



The examples given range from 11-1500 diameters. 



C5) Microscopical Optics and Manipulation. 



Entoptic Vision.f — By means of this Entoptiscope, W. F. Barrett} 

 has made further observations on the human eye especially in regard tc 

 Haidinger's Tufts, the Macula lutea, the Punctum caecum, Purkinje's 

 figures and and moving corpuscles. The entoptiscope, it will be re- 

 membered, is an instrument for the self-examination of one's eye. Its. 

 use has enabled the author not only to correct certain inaccurate ideas 

 and measurements, but to ascertain new facts. 



Eaidimjer's Tufts. — These are found to be precisely coincident with 

 the Macula lutea. 



Macula lutea. — Taking the nodal point as 16 mm. from the retina 

 the horizontal diameter of the macula was found to be * 9 mm. and the 

 vertical slightly less. The angle subtended by the yellow spot is a little 

 over 'if (not 6-8°, as some authorities state). 



Punctum ccecum and Purkinje's Figures. — The instrument lends 

 itself admirably to observation of these plienomena. 



Moving Corpuscles. — The author's observations favour the view that 

 these are white blood-corpuscles, either in the retinal vessels or migrating 

 from the capillaries. The rapidly moving points of light which are 

 seen may be due to those corpuscles which are near the walls of the 



* Journ. Quekett Micr. Club, ix. (1906) pp. 429-30 (2 figs, and 3 pis.) ; also in 

 extract form. 



t Sci. Proc. of Roy. Dublin Soc, xi. (1906) pp. 111-36 (8 pis.). 

 X See this Journal, 1906, p. 405. 



