DISINFECTANT 43 



agent in tar, which, either in its ordinary state or burnt as a fumigator, has always 

 hold high rank amongst disinfectants. Pitch and tar were the most popular medi- 

 cines in use against the cattle plague when it visited this island in the last century; 

 the animals being preserved against contagion by having their noses and jaws rubbed 

 with tar, whilst the cowhouses were disinfected by burning pitch and tar in them (in 

 which process a certain quantity of the vapours of carbolic acid would escape combus- 

 tion). The almost universal custom of burning gum resins and odoriferous woods in 

 connection with religious ceremonies may have originally arisen from the disinfecting 

 powers of the creosote m the smoke. The well-known efficacy of smoke in preserving 

 meat is entirely due to the presence in it of this agent. 



1 Pitch oil, oil of tar, and similar products owe their value entirely to carbolic acid. 

 This body may, in fact, be called the active principle of tar, just as quinine is 

 the active principle of bark, or morphia of opium, and it has the great advantage of 

 being easily prepared in any country where coal or wood can be obtained.' 



After describing some experiments with sulphurous acid, Mr. Crookes proceeds to 

 describe some made by himself with carbolic acid : 



' A piece of fresh meat was soaked in a one-per-cent. aqueous solution of carbolic acid 

 for one hour; it was then wrapped in paper and hung up in a sitting-room in which 

 there was a fire almost daily ; at the end of ten weeks it was examined. It had dried 

 up to about one-fourth of its original size, but looked and smelt perfectly good and 

 fresh, a very faint odour of carbolic acid being all that was perceptible. It was soaked 

 for twenty-four hours in water, and then stewed with appropriate condiments and 

 eaten ; it was perfectly sweet, and scarcely distinguishable from fresh meat, except by 

 possessing a very faint flavour of carbolic acid, not strong enough to be unpleasant. 



' Animal membranes in the forms of gut, skin, and bladder, were perfectly preserved 

 if immersed direct in aqueous solution containing 1 per cent, of carbolic acid ; but if 

 previously moistened with water, and then immersed in dilute carbolic acid, the 

 preservation of the skins was not so complete. 



' Animal size and glue, mixed, in the form of solution, with small quantities of car- 

 bolic acid, were perfectly preserved from change even in hot weather. 



' These are important experiments. They point out in a striking manner the differ- 

 ence between mere deodorisers and antiseptics. Hitherto attention has been almost 

 entirely confined to the deodorisation of gases arising from putrescence. The effect 

 has been combated, whilst the removal of the cause has received scarcely any attention. 

 Chloride of lime, one of the strongest of the class of deodorisers, acts, as has been 

 shown, only on the gases of existing putrefaction, but it has no influence over the 

 future. Carbolic acid, on the other hand, has scarcely any action on the fetid gases ; 

 but it attacks the cause which produces them, and, at the same time, puts the organic 

 matter in such a state that it never re-acquires its tendency to putrefy. 



' It became now a matter of considerable interest to ascertain in what way carbolic 

 acid acted in arresting decomposition, and the following experiments were made, with 

 the object of clearing up this point : 



1 Albumen was mixed with four times its bulk of water, and a one-per-cent. solution 

 of pure carbolic acid was added to it. No change took place for the first few minutes, 

 but after a little time a white cloudiness was formed, which gradually collected to- 

 gether into a coagulum. On separating this, and exposing it freely to the air, it 

 entirely resisted putrefactive decomposition. The solution strained from the coagulum 

 still contained carbolic acid and uncoagulated albumen. 



' The same experiment was repeated with pure cresylic acid. This acid had still 

 less affinity for albumen, the mixed solutions remaining clear for nearly half-an hour. 



1 It is evident, therefore, that the tar acids do not owe their special action to their 

 coagulating powers on albumen, for the last two experiments show, contrary to the 

 generally received opinion, that their affinity for this body is but slight. 



' A few drops of carbolic acid, added to half a pint of sugar syrup, and yeast in full 

 action, immediately put a stop to the fermentation. 



Fresh brewers' yeast was washed with a solution of one per cent, of carbolic acid, 

 and then with water. Its power of inducing fermentation in a solution of sugar was 

 entirely destroyed, although no perceptible change in the appearance of the yeast-cells 

 could be detected under the microscope. This experiment was repeated several times, 

 and always with the same result, although when the yeast was simply washed in water 

 it readily induced fermentation. 



' The odour of carbolic acid adhered most pertinaciously to the yeast, and by no 

 ordinary amount of washing and exposure to the air could it be removed. 



1 Strychnine was added to a mixture of yeast and sugar solution in full fermenta- 

 tion. No visible effect was produced, the evolution of carbonic acid continuing as brisk 

 as before. 



The above experiments, some of which were performed by my friend Mr. Spiller, 



