720 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



Fig. 170. 



Device for Levelling the Microscope.* — T. 0. Beynolds shows the 

 ingenious device (fig. 170) for levelling a Microscope when used for 

 liquid preparations. The expense of a spirit-level may he saved by 

 means of a glass slip on which are placed a few drops of water con- 

 taining particles of opaque material. The 

 apparatus is levelled by means of the 

 three screws, and the desired position is 

 indicated when currents are no longer 

 perceptible. 



Method for Demonstrating the Struc- 

 ture of Bacteria.! — In his researches 

 on the structure of bacteria, Prof. K. 

 Nakanishi adopted the same method which 

 be found suitable for the demonstration 

 of the malaria parasite. This method 

 consists in making a film of the stain on 

 a slide. A saturated aqueous solution of 

 methylen-blue is deposited on a slide and 

 allowed to dry. In this way a thin layer 

 of pigment is formed. A droplet of blood 

 is deposited on a cover-glass, and the 



Fluids con- 



"Microscofe Foot. 



a Threaded hole for leveling screw. 



A Microscope pillar. 



A . End view of microscope foot. 

 £. Milled head of leveling screw 



latter on the staining film. 



taining bacteria are treated in a similar 



way. Bouillon cultures are the most 



suitable. Cultivations on solid media 



require to be suspended in some fluid in which the pigment is easily 



soluble. For methylen-blue, blood-serum, ascitic fluid, &c, may be used. 



The author, however, found that distilled water answered very well. 



Klein's Method of Counting Bacteria, and some Applications 

 thereof.^ — This method consists in mixing 0-1 to 1 ccm. of the fluid 

 containing bacteria with the same quantity of staining fluid. After the 

 lapse of a minute a portion is removed with a platinum loop of known 

 size. A film smeared on a cover-slip is dried and mounted in the usual 

 way. The number of bacteria in a cubic centimetre was calculated after 

 counting 50 fields under the Microscope. For this purpose it is necessary 

 to know how many fields go to 1 square centimetre of cover-glass. 



F. H. Hehewerth made the number to be 5656. The author contrasts 

 the results obtained by this method with Koch's plate method, and finds 

 that Klein's procedure gives a greater number of organisms ; this may 

 be accounted for by the fact that when a preparation is stained after being 

 fixed, a large number of bacteria are washed away. For fluids which 

 contain few bacteria Klein's method is not to be recommended, and a 

 perfect method of counting bacteria has yet to be devised. 



The author employed the method for determining the duration of 

 bacterial generations, and their increase in certain periods of time on 

 different media and at different temperatures. 



The author measured the size of bacteria, and found that the length 

 and breadth were extremely variable even in quite fresh cultures. 



By comparing the results of the Klein and Koch procedures, the 



* Journ. Applied Microscopy, iv. (1901) p. 1458 (2 figs.), 

 t Centralbl. Bakt., 1" Abt., xxx. (1901) pp. 98-102. 

 % Op. cit.. xxix. (1901) pp. 72-3 and 914. 



