32 BACTERIOLOGY. 



There is no wider field for research than the determination of 

 the real effect of disinfectants and antiseptics. Painstaking and 

 laborious as the researches are which have been hitherto made, the 

 subject is so beset with fallacies, leading, in some cases, to totally 

 erroneous conclusions, that it is not surprising that one meets on 

 all sides with conflicting statements. The author has no intention 

 of analysing these results, but a general idea will be given of the 

 methods which have been employed, and for further details reference 

 must be made to the original papers mentioned in the bibliography. 



Chemical Substances. It was customary to judge of the power 

 of a disinfectant or antiseptic by adding it to some putrescent liquid. 

 A small portion of the latter was, after a time, transferred to 

 some suitable nourishing medium, and the enicacy of the substance 

 estimated by the absence of cloudiness, odour, or other sign of 

 development of bacteria in the inoculated fluid. Koch pointed out 

 the errors that might arise in these experiments from accidental 

 contamination, or from there being no evidence of the destruction 

 of spores, and we are indebted to him for a complete and careful 

 series of observations with more exact methods. 



Instead of employing a mixture of bacteria, Koch's plan was to- 

 subject a pure cultivation of some well-known species with marked 

 characteristics to the reagent to be tested. A small quantity was 

 then transferred to fresh nourishing soil, under favourable con- 

 ditions, side by side with nutrient material inoculated from a 

 cultivation without treatment with the disinfectant. The latter 

 constituted a control test, which is most essential in all such 

 experiments. To test the resistant power of bacteria which are 

 easily destroyed, two species were selected, Micrococcus prodigiosus r 

 and the bacillus of blue pus. These were cultivated on potatoes r 

 the surfaces of which were sliced off and dried. A fragment trans- 

 ferred to freshly prepared potato gave rise to a growth of the 

 particular micro-organism ; but if after treatment with some reagent 

 no growth occurred, the conclusion was drawn that the reagent wa& 

 efficacious in destroying the vitality of the bacteria. 



Anthrax bacilli in blood, withdrawn from an animal just killed, 

 were taken to represent sporeless bacteria, while silk threads steeped 

 in an artificial cultivation of the bacilli and dried, afforded a means 

 of testing the vitality of spores. 



Even by employing pure cultivations on solid media, great 

 precautions were necessary to avoid mistakes. When, for instance, 

 .1 l;n-^c quantity of the growth which had been subjected to some 

 chemical solution was carried over to the fresh tube containing 



