400 Profs. Percy Frankland and Marshall Ward. 



development of the latter, the B. coli communis has shown itself to be 

 possessed of greater powers of resistance than the typhoid bacillus 

 itself. Hence, although the addition of various chemical substances 

 in suitable proportions may effectually destroy or retard the growth 

 of other organisms, yet the B. coli communis survives and remains 

 present along with the typhoid bacillus ; indeed, in many cases it has 

 been shown that such additions have actually destroyed the typhoid 

 bacillus, and left the B. coli communis alone master of the field. It is 

 true that, growing in artificial cultures side by side, there are certain 

 differences observable between these two organisms, for the B. coli 

 communis grows more luxuriantly in the various culture-media em- 

 ployed than does the typhoid bacillus, or to use the expressive 

 language of a French observer, the B. coli communis grows as though 

 it were well, and the typhoid bacillus as though it were ill; but yet 

 on the gelatine plates of each there are nearly always colonies which 

 are indistinguishable from those of the other, whilst even in the 

 potato-cultures, which used to be regarded as the crucial test for the 

 typhoid bacillus, the B. coli communis may and does exhibit, under 

 certain conditions, growths which resemble in every respect those 

 produced by the typhoid bacillus. In two media, however, as has 

 been pointed out by D unbar (" Ueber den Typhusbacillus und den 

 Bacillus Coli Communis," ' Zeitsch f. Hygiene,' 1892, 491), a 

 marked difference is found in the behaviour of these two organisms. 

 Thus, when inoculated into sterile milk, the typhoid bacillus renders 

 the liquid slightly acid, but never causes its coagulation ; the B. coli 

 communis, on the other hand, at the temperature of the body coagu- 

 lates the milk in from 24 48 hours, rendering it at the same time 

 strongly acid. Again, when grown in sterile fluid meat extract or 

 broth, the B. coli communis at 37 C. produces, in the course of from 

 3 12 hours, a quantity of gas (consisting of hydrogen and carbonic 

 anhydride), whilst no formation of gas has, under the same conditions, 

 ever been observed in the case of the typhoid bacillus. 



This latter mode of distinguishing between the B. coli communis 

 and the typhoid bacillus I have reduced to the following extremely 

 simple and handy form suitable for their rapid differentiation : The 

 organism under investigation is inoculated into a test-tube containing 

 ordinary gelatine peptone in a melted state, the latter is shaken to 

 distribute the bacilli throughout the liquid, which is then allowed to 

 solidify and maintained at the ordinary temperature (18 20 C.). 

 The tube, if it contains the B. coli communis, will invariably, after 

 12 48 hours, exhibit numerous conspicuous gas bubbles distributed 

 through the solid medium, whilst no such bubbles make their 

 appearance in similar tubes containing the typhoid bacillus. The 

 test possibly depends upon the meat extract containing sufficient 

 dextrose (derived from the post-mortem transformation of the glycogeu 



