ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 469 



Orienting Small Opaque Objects.* — Dr. E. W. Hoffmann, after men- 

 tioning bis metbod of orienting very small objects,f states that opaque 

 objects imbedded in collodion-clove-oil mixture can be oriented easily if 

 tbo procedure be carried out in 90 p.c. alcohol. When objects are diffi- 

 cult to cut as well as opaque — such as embryos of worms, insects' eggs, 

 eggs and embryos of certain mollusca — be advises that the specimen 

 should first be saturated with thick celloidin and afterwards the mass 

 treated with oil of cloves. The objects are then placed on a slip of 

 glass and oriented under 90 p.c. alcohol. 



Employment of Projection Apparatus for Demonstrating Vital 

 Processes.} — Prof. W. Pfeffer advocates the use of a projection apparatus 

 for demonstrating vital processes of living organisms to large classes. 

 The apparatus employed is constructed by several firms, to whose cata- 

 logues reference should be made for particulars as to the details. 



The most interesting feature in the author's arrangement is for cool- 

 ing the light. This is in the first place passed through a tank of water 

 200 mm. thick, kept cool by means of ice. In order to decrease the 

 heat still further the light is also filtered through a nearly saturated 

 solution of iron sulphate, by which most of the heat rays are removed. 



Although some of the light rays are extinguished in the process, 

 there is ample illumination even for high magnifications. The distance 

 required varies from 3-4^ metres both for micro- and macro-projection. 

 Suitable carriers are provided for adapting the different preparations 

 to the apparatus, and an erecting arrangement converts the reversed 

 position of the specimen into the natural. 



The apparatus is adapted for demonstrating swarming movements, 

 galvanotaxis, the streaming of protoplasm, plasmolysis, growth, and 

 various movements in plants. 



Bacteriological Examination for Diphtherial — Dr. L. Cobbett 

 states that, as the result of a very large number of bacteriological ex- 

 aminations (950), when one has become well acquainted with the range 

 of the morphological variation of the diphtheria bacillus, it is fairly 

 easy to distinguish it from all others (that is, if the acid-producing hut 

 non-virulent bacillus which resembles the Loeffler bacillus in all other 

 ways, be admitted as an attenuated diphtheria bacillus). The bacillus 

 of Hoffmann is the only one which presents any difficulty, and this 

 could, as a rule, be excluded on morphological grounds alone. In 

 cases of difficulty the formation of acid in glucose media appears to 

 be the final test to distinguish between the true diphtheria bacillus, 

 whether virulent or non-virulent, and the pseudo-bacilli. The medium 

 used was alkalised serum to which 1 p.c. of glucose was added. Both 

 horse and ox serum were used. The earliest visible growth of diph- 

 theria bacilli was observed in six hours, and the latest in three days. 

 For staining, Loeffler's methylen-blue was used, diluted with two or three 

 volumes of water, the cover-glass preparations being mounted in the 

 staining fluid. The groups of bacilli decolorised the fluid around them, 



* Zeitsch. f. wise. Mikr., xvii. (1900) pp. 443-9. 



t See this Journal, 1899, p. 238. 



% Pringsheim's Jahrb. f. wiss. Bot., xxxv. (1900) pp. 711-45 (7 figs.). 



§ Journ. of Hygiene, i. (1901) pp. 235-59 (3 pis.). 



