370 SUMMARY OF CURRENT RESEARCHES RELATING TO 



(d) It accounts for the appearances of edges of a transparent object,, 

 and of transparent isolated objects, as bacilli, &c. 



(e) The dimensions of the perforations, particularly the relation of 

 depth to width, account in the simplest way for the fact that sometimes 

 the white dot is seen above and the black below, sometimes vice versa. 

 It is simply a matter of an extra reflection at the wall. 



(/) Different dimensions of the perforations explain the varying 

 vertical distances between the black aud white dots seen in different 

 diatoms on the same slide. 



(g) Lastly, the existence of patches on a diatom showing reverse 

 order of the black and white dots can be accounted for by the difference 

 of refractive index of the gum or other medium in which that portion 

 of the dir.toin forming the patch is immersed. 



B. Technique."" 

 CD Collecting- Objects, including- Culture Processes. 



Cultivation of Anaerobic Bacteria, j — Dr. Hammerl has elaborated 

 a method for completely eliminating oxygen from anaerobic cultivations, 

 and of obtaining oxygen-free nutrient media. Taking advantage of the 

 fact that solutions of methylen-blue are colourless if every trace of 

 oxygen is removed therefrom, he used this substance as an indicator, 

 and added small quantities to his glucose-formate nutrient media. By 

 prolonged heating in a water-bath or steamer he found he was able to 

 drive off the dissolved oxygen from the depths of the medium in the 

 tubes, although a coloured ring, some 1*5 cm. broad, at the upper part 

 indicated the presence of oxygen at the surface. 



On testing the various methods in general use for the production of 

 a condition of anaerobiosis by means of the methylen-blue, all were 

 found to be defective, traces at least of oxygen always being present in 

 the media. He then employed fresh solutions of ammonium sulphate 

 as the deoxidising agent. This substance does not inhibit the growth 

 of bacteria, and if freshly prepared in the manner described by the 

 author, gives highly satisfactory and concordant results. 



The method described for preparing the fresh ammonium sulphate 

 is as follows : — Fill 100 to 150 ccm. distilled water into a stoppered 

 measuring cylinder, replace the stopper by a cotton- wool plug, and 

 sterilise in the steamer together with a piece of glass tubing long enough 

 to reach to the bottom of the measure, and some rubber tubing. When 

 cool connect the glass tube to a reservoir of sulphuretted hydrogen gas 

 by means of the rubber tubing, and pass the gas through the sterile 

 water in the measuring cylinder for five or six minutes. Now fill exactly 

 10 ccm. of the H.,S water into each of several test-tubes (6 or 8), and 

 add to the first tube 2 drops of a 1 p.c. solution of ammonia, to the 

 second 4 drops, and so on, shaking each thoroughly to mix the contents. 

 Finally add 3 drops of a concentrated alcoholic solution of methylen- 

 blue to each tube, and note the length of time required to decolorise the 



* This subdivision contains (1) Collecting Objects, including Culture Pro- 

 cesses ; (2) Preparing Objects ; (3) Cutting, including Imbedding and Microtomes ; 

 C-t) Staining and Injecting ; (5) Mounting, including slides, preservative fluids, &c. ; 

 (6) Miscellaneous. * f Centralbl. Bakt., 1" Abt., xxx. (1901) pp. 658-61. 



