240 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
The exact position of these bands is determined once for all, and the 
displacements which they undergo when the wedge is superposed, first 
so as to augment the effect of the plate, and secondly so as to subtract 
from it. 
The difference of path of the system will be in the first case 
0 = 0 + 6 ', 
in the second, 
0 = 0 — 0 ', 
O' being the constant difference produced by the plate, 0 the variable 
one caused by the wedge. But we have 
O' = D' 8, 
where D' is the known thickness of the plate, and 
0 = D8. 
Therefore, 
The author’s determinations of the thickness at different points of the 
ordinary wedges offered lor sale showed how very irregular was their 
form. 
The method of using the birefractometer is very simple and convenient. 
The crystal section under examination is orientated so as to give the 
maximum brightness between crossed nicols, and the birefractometer is 
then slid in beneath the analyser until the doubly refracting body is 
obscured as completely as possible. When this happens, the difference 
of path produced by the crystal is exactly compensated by that caused 
by the wedge. The division on the latter at which the compensation 
takes place is then noted, and thus from the table giving the constants 
which accompanies each instrument, the exact value of the interference 
tint exhibited by the crystal, in the thickness of the layer of air of the 
Newton’s rings corresponding to this tint, can be determined. 
j8. Technique.* 
(1) Collecting Objects, including Culture Processes. 
Ilosvay’s Reagent as a Test for Cholera Bacilli and other 
Bacteria.j — Dr. M. Lunkewicz finds that Ilosvay’s reagent is an 
extremely sensitive test for the nitrous acid produced by cholera bacilli 
and some other organisms. The reagent is composed of two fluids kept 
apart and mixed in equal volumes when required for use : — I. Naphthyl- 
amin 0*1; aq. destill. 20*0; acid, acetic, dil. 150 • 0. II. Acid, sulphanilici 
0*5; acid, acetic, dil. 150*0. The naphthylamin is boiled with water, 
and, after standing, the supernatant clear fluid is decanted off, and then 
the acetic acid added. 
To bouillon or pepton cultures about one-fifth of their bulk of the 
* This subdivision contains (1) Collecting Objects, including Culture Pro- 
cesses ; (2) Preparing Objects ; (3) Cutting, including Imbedding and Microtomes; 
(4) Staining and Injecting ; (5) Mounting, including slides, preservative fluids, &c. ; 
(6) Miscellaneous. f Centralbl. f. Bakteriol. u. Parasitenk., xvi. (1894) pp. 945-9. 
