640 SUMMARY OF CURRENT RESEARCHES RELATING TO 



flask with a litre of distilled water and 30 grm. of pepton. The flask is 

 then heated in an autoclave for 1/4 hour. The contents are then poured 

 into another flask which contains 120-150 grm. of gelatin. After the 

 gelatin is dissolved, some soda is added to render it slightly alkaline. It 

 is then kept for 1/4 hour in an autoclave at 110°, after which it is acidi- 

 fied with a deminormal solution of H 2 S0 4 in such wise that the acidity 

 of 10 ccm. of the gelatin is neutralised by • 2 ccm. of a deminormal 

 solution of soda. This acidity is equivalent to • 5 of H 2 S0 4 per litre. 

 The mixture is again heated for 8-10 minutes, filtered, and the acidity 

 tested with phenolphthalein and deminormal soda solution. If red colour 

 appears when 0*2 ccm. of soda solution have been added to 10 ccm. of 

 the gelatin, the magnesium sulphate may be added in the proportion 

 of 2*5 per litre of gelatin. The mass is then distributed into tubes 

 (10 ccm. each) and sterilised thrice. When about to be used, 1 ccm. 

 of a 35 per cent, solution of lactose and 0-1 ccm. of a 2-5 per cent, 

 solution of phenol are introduced into each tube. 



This medium is stated to give very certain results for isolating the 

 typhoid bacillus from stools in the presence of B. coli, more especially 

 in the earlier stages of the malady. 



Neutralisation of Media.* — Dr. Eyre, after calling attention to the 

 important influence exercised by the reaction of the medium upon the 

 growth of an organism cultivated thereon, advocated the adoption of 

 media (broth, gelatin, and agar) of a definite " standard " reaction for 

 ordinary laboratory use, and pointed out that litmus, the indicator 

 chiefly used in this country, was totally unsuited for exact work, as it 

 was not sufficiently sensitive to weak organic acids and acid phosphates. 

 Phenolphthalein, however, was a sensitive and reliable indicator, and 

 gave a sharp and definite " end-point." At the meeting of the Patho- 

 logical Society at Cambridge, Dr. Eyre exhibited a series of flasks of 

 agar and gelatin, demonstrating the colour produced when the end-point 

 or neutral point to phenolphthalein was reached, and showing the marked 

 effect of the addition of minute quantities of decinormal solution of 

 caustic soda to the medium after that point had been reached, an effect 

 which proved that it was hardly possible for the most inexperienced 

 worker to make a greater error than 5 per cent, when titrating with 



N 



, ^ NaOH, and using phenolphthalein as the indicator. 



Apparatus for Making Roll-cultures.f — Dr. G. H. F. Nuttall has 

 devised a convenient apparatus for making roll-cultures (figs. 173, 174). 

 The principal parts are a marble block and a tin box. The upper sur- 

 face of the block is polished, and has two grooves for tubes, the section 

 of the grooves being less than a semicircle. About 1 cm. from the edge 

 is a third groove for carrying off the water which might wet the plugs. 

 In order to make the surface of the block perfectly smooth, a very thin 

 layer of melted paraffin is brushed over it and rolled smooth with a hot 

 tube. Should the layer get worn, .it is easily wiped off with a cloth 

 damped with turpentine or xylol, and a fresh film applied. The block 

 is kept in an oblique position, and prevented from touching the sides of 



* Brit. Med. Journ., 1900, ii. p. 21. 



t Centralbl. Bakt. u. Par., l te Abt., xxvii. (1900) pp. 605-9 (2 figs.). 



