REACTIONS OF B. TYPHOSUS AND B. COLL 307 



which is somewhat difficult, is as follows. Fresh milk is slightly 

 warmed, and sufficient very dilute hydrochloric acid is added to cause 

 precipitation of the casein, which is now filtered off. Dilute sodium 

 hydrate solution is added up to, but not beyond, the point of neutralisa- 

 tion, and the fluid steamed for one to two hours, by which procedure 

 any casein which has been converted into acid albumin by the hydro- 

 chloric acid, is precipitated. This is filtered off, and a clear, colourless, 

 perfectly neutral fluid should result. Its chief constituent, of course, 

 will be lactose. To this, 5 per cent of a saturated alcoholic solution of 

 litmus is added, the medium is put in equal quantities into tubes and 

 then sterilised. After growth has taken place, the amount of acid 

 found can be estimated by dropping in standardised soda solution/ till 

 the tint of an uninoculated tube is reached. 



I W ^> 



By any of these media the undoubted capacity ot. tjie 

 B. coli to ferment lactose can be demonstrated. Accord- 

 ing to the first results of Chantemesse and Widal, the 

 B. typhosus did not ferment lactose. Petruschky, however, 

 states that it can do so. Much seems to depend t upon 

 what other constituents are present in the medium. 

 Petruschky noticed its acid-producing powers in litmus-whey. 

 Pere has confirmed the earlier view, but finds that the 

 typhoid bacillus, though it cannot ferment cane sugar or 

 lactose, can originate such a change in arabinose, galactose, 

 levulose, and glucose. The fermentative power of the 

 typhoid bacillus is thus, though existent, much less active 

 than that of the B. coli ; and as a matter of practical experi- 

 ence the formation of bubbles of gas in Chantemesse and 

 Widal's lactose medium is rarely observed. The test may, 

 therefore, be taken in conjunction with others, as of use in 

 diagnosing the identity of the bacillus. 



Curdling of Milk by the B. Coli. This probably depends 

 on the fermentation of the lactose of the milk, and the. 

 throwing down of the casein by the resulting lactic acid ; 

 but the action may be a more complicated one, as milk can 

 be curdled by organisms which do not possess acid-forming 

 properties. To apply this test 10 c.c. of milk are put in a 

 series of test-tubes and sterilised by steaming at 100 C. 

 It will be found here that the B. coli curdles milk, while 

 the B. typhosus does not. 



Formation of Acids in Ordinary Media. If ordinary 



