ZOOLOGY AND BOTANY, MICROSCOPY. ETC. 95 



for mounting diatoms. One of these is a solution of biniodide of mer- 

 cury in excess of iodide of potassium. Tho solution is not only readily 

 obtained, but is easily retained within a ring of Eousselet's gold-size- 

 dammar (saturated solution of dammar in benzol 2 parts, gold-size 

 1 part). Tho solution, which is colourless, brings out the structure 

 with clearness and beauty. Another colourless medium is phosphorus, 

 which has a refractive index of 2 '2. The pictures are clear and brilliant, 

 but are only obtained by tedious and difficult manipulation. Quinidino 

 is colourless and is easily manipulated ; it is only necessary to place a 

 portion along with the diatoms between the cover-slip and the slide, and 

 fuse the quinidine with a spirit-lamp. Its chief fault is that the mounts 

 soon become opaque from crystallisation of the medium. Realgar, 

 which has a refractive index of 2*5, has several drawbacks. Great heat 

 is required to fuse it, the high temperature often twists or distorts the 

 valves, and the colour of the finished mount is yellow. Another medium 

 is a mixture of piperine and bromide of antimony (3 to 2 by weight). 

 A quantity sufficient only to fill two-thirds of the area of the cover-glass 

 is placed on the slide ; the mixture is then gently heated over a spirit- 

 lamp; when the medium has set, the unoccupied margin is filled up 

 with paraffin, and the cover-glass encircled with Hollis' liquid glue. 

 This medium answers well for the finely lined species, but not for 

 Coscinodiscus or for any of the other coarse circular forms. 



(6) Miscellaneous. 



New Thermo-Regulator.* — Dr. St. Epstein has devised a thermo- 

 regulator which is not only easily filled, but can be rapidly set for 

 different temperatures. The temperature oscillations do not amount to 

 more than ' 1° C, and are quite independent of external conditions (gas 

 and air pressure). 



Demonstrating Form and Size of Bacteria, f — Dr. A. Macfadyen 

 and M. J. E. Barnard give a short account, with photographic illustra- 

 tions, of the main types of bacteria. The organisms described and 

 depicted are Streptococcus pyogenes, Staphylococcus pyogenes aureus, 

 Dip>lococcus pneumoniae, Bacillus pestis, Spirillum cholerse, Bacillus 

 typhosus, and Bacillus tetani. The magnification used ( x 1750) was 

 the same in all cases, so that by a glance at the plate the relative size 

 and characteristic appearance of the various organisms can at once be 

 grasped. The objectives used were a Zeiss 3 mm. apochromatic, and a 

 Winkel 1*8 mm. fluorite system, low-power projection-oculars being 

 used in each case, and magnification obtained by suitable camera exten- 

 sion. The organisms were all stained, and the screen used was a 

 saturated solution of acridine yellow, about 15 mm. thick. 



Apparatus for Testing Milk and for Cultivating Bacteria. J — Dr. 

 St. Epstein describes a new fermentation apparatus for testing the value 

 of milk for cheese making and also for the aerobic cultivation of bacteria. 

 The apparatus (fig. 15) consists of two parts : the vessel A for holding 

 tho milk or the nutrient medium, and B for collecting the gases. B 



* Centralbl. Bakt., l te Abt., xxviii. (1900) pp. 503-4 (1 fig.). 



t Nature, lxiii. (l'JOO) pp. 0-10 (1 pi., S figs.). 



% Centralbl. Bakt., 2 ,e Abt., vi. (1900) pp. 65S-9 (2 figs.). 



