268 



Mr. A. W. Blyth. 



[Nov. 26, 



soil — to a minimum, so that practically as soon as the micro-organisms 

 still surviving were floated into the nutrient gelatin they were 

 removed from the sphere of disinfectant influence. 



Phenol and Cresol. — It is of importance to know the relative dis- 

 infectant powers of phenol and cresol, and for this purpose the 

 following comparative experiment was made. Two quantities of 

 sewage were respectively treated with phenol and cresol, so that 

 the mixtures were equivalent to 1'9 per cent., and allowed to act for 

 twenty-four hours ; the mean of two strictly concordant experiments 

 gave the following as the number of colonies which at the end of 

 four days could be enumerated — 



No. of colonies per gram 

 of the sewage 



taken. 



Phenol 33,333 



Cresol 33,410 



The control 1,490,000 



None of the colonies in the disinfected sewage liquefied the 

 gelatin. The fungi which developed after the treatment with 

 phenol were to the other colonies as 3:5, the fungi in the cresol 

 experiment were to the other colonies as 1 : 7. Weight for weight, 

 pure crystalline phenol and pure liquid cresol seem to be about 

 equal in disinfectant power.* 



In another experiment 10 grams of phenol and 10 grams of cresol 

 were mixed respectively with 90 grams of pure calcic hydrate. 

 1 gram of each of these powders was digested with 100 grams of 

 sewage for twenty-four hours. The results of the cultivation were 

 as follows : — 



"No. of colonies per gram 

 of the sewage 

 taken. 



Phenol lime 311 



Cresol lime .... 118 



Control 1,490,000 



Ferrous Sulphate. — A saturated solution of ferrous sulphate was 

 made by boiling the crystals in water, allowing to cool, and then 

 filtering from the deposited crystals. The strength of the solution 



* Mr. J. P. Laws, F.C.S., in some recent experiments on the disinfection of the 

 Bacillus anthracis, found the relative "restraining" power of phenol and paracresol 

 to he as 2 : 3, the killing power as 2 : 5 ; hence he gives some superiority to cresol 

 as regards S. anthracis. His samples were both crystalline, and obtained from 

 Kahlbaum and made from the benzene and toluene sulphonates of potassium 

 (Fourteenth Annual Eeport Local Government Board, Supplement— Medical 

 Officer. London, 1885, p. 209) .—December 23, 1885. 



