BY C. J. POUND, F.R.M.S. 43 



means of a flattened platinum needle, portions of this film to the 

 surface of fluid media in each of the other flasks, which are after- 

 wards returned to the incuhator where they remain at 98-6 deg. 

 Fahr. for another 10 weeks. On examination at intervals during 

 this period, it will he noticed that the film, which has grown all 

 over the surface of the Huid media becomes crinkled, breaks up 

 gradually, then a new film forms, and so on, until the growing 

 bacilli have exhixnsted all the nutrient properties in the fluid 

 media, at the same time generating or setting free their poison- 

 ous products, the tuberculin. The next part of the process is to 

 carefully destroy the vitality of every bacillus in the culture and 

 then separate them from the fluid by passing the contents of 

 «ach tiask through a Pasteur-Chamberland filter, under a pres- 

 sure of 5001b. on the square inch. 



This porcelain filter, the manufacture of which is practically 

 a French Government secret, is so uniform and fine in texture 

 that the very smallest spores of bacilli or micrococci known to 

 bacteriologists cannot be forced through even under this enormous 

 pressure. 



The filtrate is now placed in a series of Florence flasks, 

 fitted with perforated rubber corks, and connected one with 

 another to a Sprengel's exhaust pump by means of glass and 

 thick -walled rubber tubing. The flasks thus connected are 

 placed in a steam sterilizer and kept heated up to a temperature 

 of 120 degrees Fahr., while the exhaust pump assists in evapor- 

 ating the contents of the flasks in vacuo until the fluid is so 

 concentrated that the glycerine, originally in the proportion 61 

 7 per cent., amounts to 50 per cent. 



The next part of the programme is the standardising, and 

 requires the greatest care and attention, inasmuch as it can only 

 be performed by a large series of physiological experiments on 

 guinea-pigs. 



The ."(O per cent, glycerine in the Anally standardised 

 Tuberculin will prevent the development of any foreign micro- 

 organisms which may gain access to the glass bottle when the 

 stopper is removed : moreover, if this material is kept in a cool, 

 dark cupboard, no alteration takes place with regard to its 

 chemical composition and its physiological eftects upon tiibercular 

 animals. 



