PROCEEDINGS OF SOCIETIES. 
95 
To examine the bacteria, though visible with ^-inch objective, 600 
diameters should be employed at least, and in dealing with the solid 
organs a softening part should be chosen ; a section made at once with 
a Valentine's knife, and the specimen be immersed in caustic potash 
and water, in which medium it is best examined, other reagents being 
applied in the usual way. 
The President had observed in putrefying infusions first spherical 
bacteria appear, and then the oval, and thought that observers were 
apt to make too many species of these bodies. 
QuEKETT Microscopical Club. 
Ordinary Meeting, November 27, 1874.— Dr. Matthews, F.E.M.S., 
President, in the chair, 
Mr. Ingpen communicated some notes on " Personal Equation," 
with reference to microscopy. He first explained the use of the term 
in astronomy, as exemplified in transit observations, and in its more 
extended application to differences by a constant quantity between 
observers, short of actual defects of vision. The same causes affected 
microscopical observation, though they were not so well recognized as 
in astronomy. The principal points referred to were the following : 
I. Mental equation, as causing differences in interpretation, parti- 
cularly with regard to test-objects. II. Nervous equation, as shown 
by varied sensibility to tremours, &c. III. Colour. Difficulty in 
estimating colour, as noted in Admiral Smyth's " Sidereal Chro- 
matics." — Eight and left eye often differ, in this respect. — Effect of 
yellow crystalline, referred to by Professor Liebreich in his lecture on 
" Turner and Mulready." — Difference in visibility of violet end of the 
spectrum, amounting in some cases to slight fluorescence. — Effect of red 
and yellow grounds in increasing definition in certain cases. — Effect 
of bluish mist caused by slight opacity of cornea or crystalline upon 
estimation of the correction of objectives. — Colour blindness often 
existing in a slight degree unsuspected, and difficult of detection. 
IV. Focal equation. Differences in effect of long and short sight upon 
cover correction, &c., also upon depth of focus, and power of resolving 
surface markings. — Differences in size of images formed by right and 
left eye, and consequent effect upon binocular vision. — Want of ac- 
commodation and pseudoscopic vision, &c. V. Form. General tendency 
of the eye to show ultimate particles circular. — Effect of square and 
triangular apertures. — Effect of astigmatism upon form, particularly of 
lines and dots, as seen in different directions. — Reference to Professor 
Liebreich's lecture. — Effects of diffraction upon points of light, &c. — 
General considerations of the effects of unnoticed differences of vision 
producing discrepancies often attributed to other causes. 
Dr. Matthews added some remarks as to the effect of quinine in 
producing fluorescence, and extending vision towards the violet end of 
the spectrum, shortening the visibility of the red end in an equal 
degree. 
