102 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
rackvvork, and this, when inserted into the suhstage support, is capable 
of being rotated ; thus the centering, focusing, and position — matters of 
importance — are secured. By both plans I have been enabled to examine 
many lined objects, whether the appearance be due to ridges, or areas 
as elevations or depressions, and I have reason to suppose, if employed 
properly and patiently, either will render visible any markings any 
objective, at least of the old school, is capable of revealing. 
The rod has been used with the 1/2, 1/5, 1/9, and 1/12 in. water- 
immersion, the latter photograjdiically, the radiant being a small 
paraffin lamp, and between it and the rod a 
Fig. 15. large No. 1 eye-j i ce, or a crossed lens, or 
a bull’s-eye condenser. After numerous 
trials, preference was given to the first. 
The white rod has also been made into 
an immersion illuminator by fixing on the 
top horizontal edge a small cover-glass 
(fig. 15). Two of the negatives accom- 
panying this were taken by it used thus, 
as an immersion illuminator ; the others 
by the blue rod, dry. 
I have been rather surprised at the 
ininutiaB either will reveal, as small bars 
of silex extending into the large areas in 
some of the fragments from the Oamaru 
dej^osit ; the secondary markings in Trice- 
ratium, &c., are remarkably well shown by 
either rod, and they well define the areas in Navicula rliomhoides, &c. 
It aj^pears to act as a narrow convergent central line of light, which, 
by careful manipulation, yields at certain points of rotation, excellent 
definition. 
Possibly what I have said will be called in question, but it must be 
understood I do not claim for the rod more than has been stated, and 
trust others, if induced to try it, may find it has not been exaggerated.” 
C4) Photomicrograpliy. 
Photomicrography.* — Dr. Th. Kilt reviews the history of photo- 
microscopy and the present condition of its technique. He describes 
in detail the apparatus of Zeiss and Klonne and Muller, light-filters, and 
orthochromatic plates ; the various cojjying methods are thoroughly 
discussed. The specimens of photography given by the author show 
the great sup>eriority of this method over drawing, and it is safe to 
prophesy that if the imf)rovements of this art can be continued, it will 
soon sweej) the field for bacteriological and histological illustrations. 
Although, from motives of economy, photozincography, which only 
imperfectly rejDroduces the delicacy of the negative, was selected, the 
illustrations given are extremely clear and sharp. 
Silver Combinations of Eosin.f — Dr. E. Zettnow finds that the 
orthochromatic power of eosin-silver plates is due to the erythrosin or 
its silver combinations, and not to the eosin. The erythrosin plates 
* ‘ Encyklojiadie cl. gesammt. Thierlieilkimde u. Thierzucht,’ Wien u. Leipzig, 
1889. Cf. Zcitschr. f. Wiss. Mikr., vi. (1889) p. 193. 
t Zeitschr. f. Wiss. Mikr., vi. (1889) p. 193, from Piiotogr. Corresiioudeuz, 1889. 
