ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 249 



formosum, in which with an axial cone the black dot image occurs 

 above the white dot (the reverse of the usual order), is structurally- 

 peculiar. He suggests that the minute perforations in this diatom are 

 silted up witli silica, and that what has been taken for special structure, 

 as seen in the black dot image, is really irregular openings in the 

 siliceous material. 



Double-Image Discs and Complementary Interference Colours.* — 

 J. Rheinberg, by placing a disc above the objective, obtains two images 

 of the same diatom in complementary colours. The disc is prism- 

 shaped, but a circular central portion has plane parallel sides. The 

 effect is to produce a direct dioptric image and a diffraction image of 

 the first order. When the dioptric image of a diatom shows colour 

 due to interference, the diffraction image shows the complementary 

 colour. 



B. Technique. t 

 CD Collecting: Objects, including; Culture Processes. 



New Method for Isolating the Typhoid Bacillus from Water.:}: — 

 ■G. Vallet takes a large quantity of water and treats it with lead nitrate. 

 The precipitate which carries down the bacteria is dissolved in sodium 

 hyposulphite and is then submitted to bacteriological examination. 

 Another method is to precipitate with alum or with barium nitrate. 

 For example, 200 ccm. of water to be tested is treated with 25 ccm. of 

 either precipitate. In 1 to 2 hours a deposit containing the bacteria is 

 formed. 



A still better method is a combination of mechanical and chemical 

 precipitation: centrifuge tubes of 20 ccm. content receive 4 drops of 

 saturated sodium hyposulphite solution and 4 drops of saturated barium 

 nitrate solution, both sterilised. After centrifuging for 3-4 minutes 

 (3000 turns) the clear fluid is decanted off, and to the sediment is added, 

 drop by drop, hyposulphite until it is dissolved. The dissolved pre- 

 cipitate is then distributed over Eisner's gelatin plates. After 3 or 4 

 days the differentiation may be begun, and for this litmus-lactose-agar 

 is recommended. Instead of this, lactose-bouillon may be used. The 

 coagulation or non-coagulation of milk should be tried and also the 

 agglutination test. 



Cultivation of the Leprosy Bacillus. § — W. J. Kedrowski success- 

 fully cultivated the microbe of leprosy from three cases ; the bacilli thus 

 obtained, however, were less resistant to acid than the leorous organ- 

 isms in the human tissues. The nutrient media used were meat-pepton- 

 bouillon and agar mixed with aqueous extract of human placenta filtered 

 through a Chamberland bougie. The media were inoculated with blood 

 and also with pieces of leprous skin. By the second or third day there 

 was a luxuriant growth in both the solid and liquid media. On gelatin the 



* Journ. Quek. Micr. Club, 1901, pp. 151-2 (1 fig.). 



t 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. J Arch. Med. expe'r. et d'Anat. pathol., 1901. 



§ Zeitschr. f. Hygiene u. Infekt., xxxvii. p. 52. See Centralbl. Bakt., 1" Abt., 

 Kef., xxxi. (1902) p. 90. 



