122 SUPPOSED INSTANCES [CH. ix 



Criticism. The last four experiments (d, e i, e ii, and e iii) 

 may be discussed together. 



In one experiment (d) B. typhosus derived from a carrier 

 apparently gave rise, in the peritoneal cavity, to a Gram-positive 

 coccus. In three experiments (e i, e ii, and e iii) B. typhosus, 

 derived from another carrier, apparently gave rise, in the peri- 

 toneal cavity, to atypical coliform organisms. 



The questions to be discussed are two whether the strain 

 of organisms isolated from the peritoneal cavity were derived 

 from the original strain of B. typhosus injected in each case, 

 and whether, if such continuity is established, the alteration 

 in character is to be regarded as a temporary variation or a 

 transmutation. 



The possibilities to be considered are (1) whether the 

 original strain of B. typhosus was pure ; (2) whether the peri- 

 toneal cavity in each case was sterile before the injection was 

 made ; (3) whether it was contaminated from the skin at the 

 time the injection was made ; (4) whether it was invaded from 

 the gut after the injection was made or after the death of the 

 animal ; (5) whether the later strain was linked up with the 

 original one by the occurrence of reversion or the discovery 

 of intermediate forms; (6) whether a repetition of the ex- 

 periments confirmed the results; (7) whether the alteration 

 in character falls within the recognised limits of variation 

 discussed in the earlier part of this work. 



(1) There are grounds for viewing the original cultures with 

 suspicion. They were not made in any instance from a single 

 organism. The urine of carrier "S" and of carrier "I," from 

 which they were isolated, admittedly contained streptococci, 

 B. coli, bacilli closely resembling B. faecalis alcaligenes and 

 other coliform organisms. These other organisms were present 

 in comparatively small numbers. In one instance it is stated 

 that B. coli and B. typhosus were present in the proportion 

 of 1 to 30,000. Such disparity in numbers might easily account 

 for the less common organisms being overlooked. It is men- 

 tioned that a change in the character of the medium, brought 

 about by simple dilution with water, enabled the associated 

 microbes to multiply so much more rapidly than the B. ly- 



