34 ADAPTATION AND DISEASE 



with Azolitmin as an indicator. He inoculated a relatively 

 large quantity of this medium with a pure culture of B. typhosus 

 obtained from the Army Medical College at Millbank, having 

 previously tested the strain and having found that it was 

 absolutely typical in its fermentation reactions (producing acid, 

 but no gas, with Glucose and Mannite, while Lactose, Saccharose, 

 Dulcite and Isodulcite gave negative results). 



Each day he made plates from the main culture upon 

 azohtmin-isodulcite-peptone-agar, with the following results : 

 The main culture in 100 ccm. of 1 per cent azolitmin dilute 

 broth showed no change until the fifth day, when the blue solu- 

 tion took on a slight change, showing that some acid was being 

 produced. At the same time the agar transplants of the fourth 

 day exhibited a pinkish tint of the medium showing beginning 

 fermentation, while the agar transplants of the fifth day at the 

 end of twenty-four hours showed a distinct pink halo around 

 every colony — as did also the plate of the sixth day. (I give 

 Major Bowman's note as Appendix II., explaining that up to the 

 last moment I hunted for the lost reference, and thus only gave 

 him time to perform the experimentum crucis. Nor indeed, 

 knowing how fully occupied he was with routine military work, 

 could I ask for or could he offer more.) 



And here is the point : add typhoid bacilli to distilled water 

 containing 1 per cent isodulcite, and they are not killed off, 

 that is to say, they undergo no greater reduction in number than 

 if added to pure distilled water. If we dealt with chance varia- 

 tion and the survival of the fittest, some of the colonies on the 

 agar at the end of four or five days would be unchanged, others 

 would show surrounding reddening of the azolitmin medium. 

 But all show the reddening. 



Here then, contrary to Bateson, we have evidence of positive 

 acquirement from without, and, contrary to the Lankesterian 

 dogma, we can so arrange our experiment as to obtain, not 

 evidence of variation in many directions, the favourable variants 

 alone surviving, but evidence that organisms placed in a given 

 environment all vary in one identical direction with clockwork 

 regularity. It is no matter of haphazard : we can of a certainty 

 induce the particular variation in a particular bacterial species. 



Or if Professor Bateson desires a perfect example of varia- 

 tion by loss of factors, we can afford him an equally telling 



