| Phenol | 1:80 | killed in 2½ minutes | ||||
| Disinfectant “A” | 1:375 | killed in 2½ minutes | ||||
| Phenol | 1:110 | killed in 15 minutes | ||||
| Disinfectant “A” | 1:650 | killed in 15 minutes | ||||
| 375 | ÷ | 80 | = | 4.69 | ||
| 650 | ÷ | 110 | = | 5.91 | ||
| 2)10.60 | ||||||
| Average | = | 5.30 | = “phenol coefficient.” | |||
Standard conditions of temperature, age of culture, medium, reaction, etc., and of making the dilutions and transfers are insisted on. Details may be found in the Journal of Infectious Diseases, 1911, 8, p. 1.
This is probably as good a method as any for arriving at the relative strengths of disinfectants and in the hands of any given worker concordant results in comparative tests can usually be attained. Experience has shown that the results obtained by different workers with the same disinfectant may be decidedly at variance. This is to be expected from a knowledge of the factors affecting the action of disinfectants above stated and from the known specific action of certain disinfectants on certain organisms (compare anilin dyes, [p. 162]).
It seems that the only sure way to test the action of such a substance is to try it out in the way it is to be used. It is scarcely wise to adopt the “phenol coefficient” method as a legal standard method as some states have done.
PRACTICAL STERILIZATION AND DISINFECTION.
The methods for sterilizing in the laboratory have been discussed and will be referred to again in the next chapter.
In practical disinfection it is a good plan always to proceed as though spores were present even if the organism is known. Hence use an abundance of the agent and apply it as long as practicable. Also it is best to secure the chemical substances used as such and not depend on patented mixtures purporting to contain them. As a rule the latter are more expensive in proportion to the results secured.
Surgical instruments may be sterilized by boiling in water for fifteen minutes, provided they are clean, as they should be. If dried blood, pus, mucus, etc., are adherent, which should never be the case, they should be boiled one-half hour. The addition of sodium carbonate (0.5 to 1 per cent.) prevents rusting. Surgeons’ sterilizers are to be had at reasonable prices and are very convenient. Whether the instruments are boiled or subjected to streaming steam depends on whether the supporting tray is covered with water or not. The author finds it a good plan to keep the needles of hypodermic syringes in a small wire basket in an oil bath. The oil may be heated to 150° to 200° and the needles sterilized in a very few minutes. The oil also prevents rusting.
Rooms, offices and all spaces which may be readily made practically gas-tight are best disinfected by means of formaldehyde by any of the methods above described ([Figs. 111] and [112]).
Stables and Barnyards (Mohler): “A preliminary cleaning up of all litter is advisable together with the scraping of the floor, mangers and walls of the stable with hoes and the removal of all dust and filth. All this material should be burned since it probably contains the infective agent. Heat may be applied to the surfaces, including barnyard, by means of a ‘cyclone oil burner.’ When such burning is impracticable, the walls may be disinfected with one of the following: