282 ORIENTAL PLAGUE chap. 



pestis introduced into a locality cannot and does not 

 carry on its existence, grow, and multiply in outside 

 nature ; but the important point is that it should be 

 prevented from gaining access to an animal body, for if 

 restricted to a saprophytic life it would soon cease to be 

 dangerous. 



The gradually diminishing capability of the attenuated 

 or rat type B. pestis (type 2) — although capable of con- 

 tinuous transference from rat to rat — to infect human 

 beings, as has been exemplified in several instances (see 

 previous chapters), would ultimately lead to cessation of 

 infection of the human subject. 



3. Chemical Disinfectants. — In respect of the great 

 and constantly widening subject of the various dis- 

 infectant agents commonly employed for destroying 

 bacteria and infective microbes, it has to be remembered 

 that laboratory experiments in which pure cultures of one 

 or the other microbe are exposed for a stated time to the 

 action of a given agent are not exactly analogous to what 

 occurs in practice when infective materials in the form of 

 secretions, excretions, and tissues of an infected animal 

 body are subjected to disinfection. I have shown this by 

 direct experiments both with regard to Staphylococcus 

 aureus and coli-typhoid bacilli. I quote in illustration 

 a paper which I published in the British Medical Journal, 

 July 2, 1904 :— 



The usual method of testing and comparing disinfectants consists 

 in exposing for a given time cultures or emulsions of a particular 

 microbe to dilutions of the disinfectant. This, no doubt, is of value 

 in comparing with one another various disinfectants or their 

 dilutions, and although it affords a sufficiently reliable index of the 

 efficacy and power of a given disinfectant in a definite dilution and 

 for a definite time exposure, it cannot, for reasons to be mentioned 



