CHAPTER 5 



THE RESISTANCE OF BACTERIA TO PHYSICAL AND CHEMICAL 

 AGENTS: DISINFECTION 



Introductory 



The early investigations of the problem of disinfection, which may be said to 

 have commenced with Pringle's observations in 1750, were largely concerned with 

 a study of the efficacy of various substances in hindering putrefaction. A century 

 and a quarter later Bucholtz (1875), using as his medium an infusion of tobacco 

 leaves, conducted a series of investigations on disinfectants ; and Baxter (1875), 

 working with vaccine lymph and glanders nodules, showed the influence of organic 

 matter in diminishing the activity of disinfectants. 



The next advance, illustrating the importance of technique, was made by 

 Koch in 1881, when he introduced an exact method of comparing the germicidal 

 power of different substances. In place of fluids swarming with different organisms 

 of varying resistance, he tested the action of disinfectants on pure cultures of 

 bacteria of approximately equal resistance. By drying anthrax spores on silk 

 threads of the same length, immersing them in a solution of the substance to be 

 tested, and subsequently transferring them to a nutrient medium in order to 

 ascertain if the bacteria were still alive, he collected a considerable quantity of 

 information on the relative activity of different disinfectants. His work was 

 criticized and his methods improved by Geppert (1889, 1891a, b). In 1897 Kronig 

 and Paul published their classical paper, describing a new method for the quan- 

 titative study of disinfection, and demonstrating that in a culture submitted to 

 the influence of a germicidal agent bacteria die, not simultaneously, but in an 

 orderly sequence. To Madsen and Nyman (1907) and to Chick (1908, 1910, 1912) 

 must be ascribed the merit of analysing the various factors upon which disinfection 

 depends, and of showing that the law underlying the death of bacteria is similar 

 to that underlying a simple unimolecular chemical reaction. 



Starting from empirical observations on the preservation of dead human bodies, 

 the study of disinfection has progressed through the qualitative stage to the quan- 

 titative stage, and has now reached a point when the ultimate solution of the 

 problem lies in the domain of the physical chemist. 



The subject of disinfection is large, and can be treated from different aspects. 

 In the present chapter we shall make no attempt to deal with it exhaustively ; 

 on the contrary, we shall purposely neglect a considerable part of the subject 

 dealing with the use of germicides in practice, as we consider this to fall within 

 the province of the hygienist. Our main endeavour is to discover as far as possible 

 the underlying principles of disinfection, to discuss the laws governing the killing 

 of bacteria, and to point out the importance of a thorough knowledge of these 



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