118 SUPPOSED INSTANCES [CH. ix 



rests with the claimant. If it is possible to show that he has 

 failed to exclude a single possible source of error, a verdict of 

 not proven must be returned. 



When considering the value of evidence adduced in sup- 

 port of supposed instances of variation or transmutation (vide 

 Chap. Ill) we mentioned various sources of error. Bearing these 

 in mind, and also the wide limits within which we have found 

 variation may occur (vide Chaps. IY-VII) we will now consider 

 in detail the processes by which Major Horrocks obtained the 

 results he claimed and the value of the evidence he brings 

 forward to support his contentions. 



(a) The alteration of B. typhosus to an organism inter- 

 mediate between B. typhosus and B. coli. 



(Page 246.) A strain of B. typhosus was isolated from 

 the urine of a typhoid carrier " TS " from whose blood a pure 

 culture of B. typhosus had previously been obtained. After 

 3 days' incubation on bile salt glucose litmus agar the strain 

 gave the typical reactions of B. typhosus. At the end of a 

 week, however, the following characters were displayed : lac- 

 tose, salicin and dulcite were rendered slightly acid, broth 

 gave a marked indol reaction, the neutral red reaction yielded 

 a slight yellow colouration, the organism appeared only slightly 

 motile and was not agglutinated by anti-typhoid serum. The 

 organism, however, gave rise to typhoid agglutinins when 

 injected into a rabbit, and this rabbit's serum deviated com- 

 plement in the same manner as a known antityphoid serum, 

 and the organism further had the power of absorbing the 

 specific agglutinins from a known typhoid serum. 



After 4 passages through the guineapig the organism lost 

 its lactose fermenting property and only differed from the 

 original B. typhosus by forming a trace of acid in salicin. 

 After 4 further passages it reverted to the unusual fermenting 

 type described. 



The urine of carrier " TS " from which the strain was origin- 

 ally derived was again carefully tested but only typical typhoid 

 organisms were obtained. 



Criticism. We have already quoted (vide p. 11) instances 

 of the occurrence of organisms, derived in some cases from 



