October 16, 1885.] 



sciEJS-cm 



329 



it synonymous with deodorization. From our 

 point of view the destruction of sulphuretted hydro- 

 gen, or of ammonia, in a privy vault is no more 

 disinfection than is the chemical decomposition of 

 these gases in a laboratory experiment. But when 

 we destroy the infecting power of vaccine virus, 

 or of the blood of an animal dead of anthrax, we 

 disinfect this material no matter where it may be. 

 "There can be no partial disinfection of such 

 material ; either its infecting power is destroyed or 

 it is not. In the latter case there is failure to dis- 

 infect. Nor can there be disinfection in the 

 absence of infectious material" (Prehminary report 

 of committee on disinfectants of the American 

 public health association). 



Using the term then, in tliis resti'icted and 

 scientific sense, what tests have we of disin- 

 fection, and what are the best disinfectants ? The 

 evidence of disinfection must evidently be based 

 upon experiments which show that the infectious 

 material has lost its specific infecting power. 

 Such evidence we obtahi from three sources : (a) 

 practical experience in the use of disinfectants ; 

 (h) inoculation experiments upon susceptible ani- 

 mals ; (c) biological experiments upon pathogenic 

 micro-organisms — the test being failure to multi- 

 ply in a suitable culture-medium after exposure to 

 the disinfecting agent in a given proportion for a 

 given time. 



Until g-uided by exact data obtained in the labo- 

 ratory the progress of our knowledge relating to 

 disinfection was slow and uncertain. While agents 

 now recognized as efficient were frequently re- 

 sorted to in the pre-scientific period, they were 

 often used by the sanitary authorities of the day 

 in amounts enthely inadequate for the accomplish- 

 ment of the object in view ; and for the vulgar a 

 disinfectant was a charm which was supposed to 

 exorcise the disease-producing agent in some mys- 

 terious way. We must accord a certain value to 

 the experiments of sanitarians in then* efforts to 

 restrict the extension of infectious diseases, 

 although the evidence of successful dismfection 

 offered by ' practical ' men will not always stand 

 scientific criticism. When a house in which a case 

 of small-pox has occurred is fumigated with sul- 

 phurous acid gas, and this fumigation is followed 

 by a thorough cleaning up, a Hberal apphcation of 

 w^hitewash, and vaccination of everyone in the 

 vicinity, it must always remam a matter of doubt 

 whether the small-pox infection was, or was not, 

 destroyed by the fumigation. In experiments made 

 in practice — either clmical or sanitary — we have 

 rarely any comparative test, and an undue value is 

 often accorded to negative evidence. Laboratory 

 exjjeriments are, therefore, essential as a check upon 

 ^exjjerience,' and as a guide for successful practice. 



Many experiments have been made directly upon 

 infectious material, without reference to the exact 

 nature of the infectious agent present in this mate- 

 rial — the test of disinfection being failure to infect 

 susceptible animals after treatment with the dLsin- 

 fectmg agent. Of this nature were the experi- 

 ments of Davaine upon the blood of animals dead 

 with anthrax, or with infectious septicaemia ; of 

 Baxter and of Vallin upon the virus of glanders ; 

 of the writer upon septicaemic blood ; and of 

 numerous observers upon vaccine virus. The ex- 

 periments upon dried vaccine — upon ivory points 

 — are among the most satisfactory of these ; for 

 the inference seems to be quite safe, that whatever 

 will destroy the specific infecting power of tliis 

 material will also destroy the small-pox virus. 

 The writer's experiments (1880) show very con- 

 clusively that chlorine and sulphurous acid gas are 

 agents which may be relied upon for the destruc- 

 tion of the infecting power of this material — due 

 regard being paid to the necessary conditions 

 relating to quantity and time of exposure. 



Since it has been demonstrated that the infect- 

 ing power of certain kinds of infectious material 

 is due to the presence of micro-organisms, numer- 

 ous experiments have been made to determine the 

 exact germicide power of a variety of chemical 

 agents, as tested by these demonstrated disease- 

 germs, and by non-pathogenic organisms belong- 

 ing to the same class. These experiments show 

 that, while the resisting power of organisms of 

 this class differs within certain limits, in the 

 absence of spores, a germicide for one of these 

 organisms is a germicide for all. There is a wide 

 difference, however, between the resisting power 

 of spores, and that of bacteria in active gro\\i;h. 

 The growing plant — micrococcus, bacillus, or spir- 

 illum — is quickly destroyed by a temperature of 

 from 150° to 160° F., while the spore resists a boiling 

 temperature for several hours. Carbohc acid (2^ 

 sol.), sulphate of copper (1^ sol.), and various other 

 agents which are efficient for the destruction of 

 active bacteria, fail in concentrated solution to 

 kill spores. The experimental evidence on record 

 indicates that the following named disinfectants 

 are the most generally useful, from a practical 

 point of view ; — 



Moist heat. A boiling temperature quickly 

 destroys all known pathogenic organisms in the 

 absence of spores. A temperatui-e of 230° Fahi'. — 

 steam under pressure — maintained for ten minutes, 

 will destroy spores. 



Chloride of lime. A four per cent solution 

 quickly destroys all micro-organisms, including 

 spores. Labarraque's solution (hquor sodae 

 chlorinatae) is equally efficient when of corres- 

 ponding strength. 



