ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 30& 



rack and pinion on tho bar u. The diaphragm slide / can be rotated 

 on the ring g, and also moved excentrically by the milled head i. 

 The lenses m are attached to a slide 6. A rotating stop at k 

 prevents the condenser from being racked off the bar u unless desired. 

 A pin p serves as a guide for the condenser on the other side of 

 the stage. 



A novelty in a Continental Microscope is the iris-diaphragm N 

 (figs. 51 and 52), the first we have seen. It is made on G. Wale's 



Fig. 51. Fig. 52. 



plan ; the rotation of the cone n by c causes the pieces of which the 

 iris is composed to close or open ; o is a cap. 



Thoma's Microscope for observing the Circulation of the 

 Blood.* — This Microscope was designed by Prof. E. Thoma, to observe 

 the circulation of the blood (and especially inflammatory disturbances 

 of the cii-culation), not in frogs, but in warm-blooded animals, using 

 for the purpose the mesentery of dogs, cats, guinea-pigs, &c. For 

 this purpose a very large stage is of course necessary, with some 

 kind of heating apparatus, and it is also desirable to be able to keep 

 a stream of liquid constantly flowing over the part of the animal 

 under observation, as previously recommended by the author (see infra, 

 Thoma's frog-plate). 



The instrument as now made by Herr Jung of Heidelberg, is 

 shown in fig. 53. It consists of a stout iron stand, with a wooden 

 top 19^ X 10 in., which forms the base plate of the stage. The 

 Microscope keys into the lower part of the frame by a stud pin 

 beneath the standard, so that it can be removed as required. The 

 mirror is attached to the front foot of the tripod of the Microscope. 

 On the wooden base-plate is a second plate of wood of the same size 

 as the lower one. It is unattached, and can be moved about by the 

 hand as desired. To ease the friction, the bottom of the plate has 

 four brass-headed nails on which it moves. To maintain an approxi- 

 mate equilibrium, a cord and weight are fixed to each of the front 

 corners, the cords passing over pulleys projecting from the lower 

 plate. The latter has a horseshoe aperture just beneath the body- 

 tube, and the upper plate has a circular aperture, over which is fixed 



* Arch. f. Pathol. Anat. u. Physiol. (Virchow), Ixxiv. (1878) pp. 360-93 (1 pi.). 



