328 TYPHOID FEVER. 



meat from which they are made, and the acidity might proceed from the fer- 

 mentation of these. In media made with pure syntonin or peptone, though 

 there was an initial slight acid formation, especially with the B. coli, still in 

 the case of both organisms at the end of four days the reaction was alkaline. 

 The reaction is, therefore, probably a double one, but the resulting acidity in 

 ordinary cases may be due to fermentative changes in carbohydrates. Here 

 again the acid-forming capacities of the B. typhosus are inferior to those of the 

 B. coli. 



(2) Production of Gas by the B. coli. — ■ The production of gas 

 in various media by the B. coli can be demonstrated by any of 

 the methods described (p. ji). Shake-cultures are usually 

 employed. According to Klein the gas produced is methane. 

 We have found, however, that in a shake-culture in peptone 

 solution with 10 per cent gelatin added the B. coli produces no 

 gas, but bubbles rapidly form if the medium has added to it a 

 trace of lactose. No such development of gas occurs in a shake- 

 culture of typhoid in any of these media. 



(3^ Formation of Indol. — Among the bacteria capable of form- 

 ing indol is to be classed the B. coU. Indol can be recognised 

 in bouillon cultures of the B. coli three to four days old by the 

 usual tests {vide p. 80). As thei'e is no evidence that it can 

 produce nitrites, a small quantity^ of the latter must be added. 

 The typhoid bacillus rarely gives this reaction when growing in 

 ordinary conditions, but on the other hand, it appears that sothe 

 varieties of the B. coli fail to j)roduce it also. Peckham, how- 

 ever, has found that if the typhoid bacillus be grown in peptone 

 solution,^ after a few generations of three days each it may 

 acquire the property of producing indol. The formation of 

 indol by an organism after the first transference to peptone 

 solution from one of the ordinary media may, however, be 

 accepted as evidence in favour of the organism not being the 



1 Peckham directs this medium to be made as follows : — 



Beef muscle 225 grms. 



Trypsin 4 „ 



, , Sodium chloride 5 » 



Water i litre 



The beef as old as can be gotten, so as to avoid muscle sugar being present, is 

 chopped fine and put into 500 c.c. of water and the mixture made alkaline with 

 sodium carbonate. The vessel containing the mixture is placed upon a water bath at 

 40° C. and the trypsin is added. Digest from one to one and a half hours, again ren- 

 der alkaline and bring the mixture to the boil, strain through gauze and filter when 

 cold. The reaction of the medium must be such as to require 20-30 c.c. of a deci- 

 riormal solution of caustic soda to bring it to the neutral point of phenol-phthaleine. 



