LABORATORY STERILIZATION 277 
Phenol and the cresols are somewhat sparingly soluble m water. 
A 6 per cent aqueous solution of carbolic acid, and 5 per cent solu- 
tions of the cresols are about the limits of solubility; 3 to 5 per cent 
solutions are used for most practical purposes. Phenol and cresols 
are not only very toxic for bacteria, they are caustic and poisonous 
for human tissue as well. Stronger solutions are anesthetic, sugges- 
tive of a definite action upon nervous tissue. These substances 
appear to be readily absorbed from mucous surfaces, the skin and 
wounds. They are excreted, in part at least, through the kidneys. 
"Smoky urine," indicating an irritation of the kidney tissue, is a 
not uncommon sequel of carbolic acid poisoning. 
A 3 per cent solution of phenol is approximately equivalent in its 
disinfectant value to a 1 to 1000 solution of bichloride of mercury, 
but it does not unite readih' with proteins to form insoluble, inert 
compounds, and it is not destructive of fabrics, metals and articles 
of every-day use.^ For sputum, urine, feces, purulent discharges and 
for stained and soiled linen, a 5 per cent solution, equal in volume 
to the bulk of the material to be disinfected, is used and allowed to 
remain at least one hour before being disturbed. 
Cresols form soaps with caustic solutions, which are strongly ger- 
micidal. An excellent cresol soap may be made by adding 1 part 
by volume of cresols to an equal amount of soft soap (potash soap). 
This is stirred thoroughly and allowed to stand twenty-four hours. 
A 5 per cent aqueous solution of this preparation is nearly three times 
as efficient in its disinfectant value as a 5 per cent solution of carbolic 
acid. 
Tincture of Iodine. — In vitro, tincture of iodine is of little value as a 
germicide, but freshly prepared tincture of iodine applied to the skin 
appears to possess \'ery considerable germicidal value. The solu- 
tion seems to be most effective when it is freshly prepared, and works 
most satisfactorily when the part upon which it is to be used has been 
cleaned with alcohol and allowed to dry. Nascent iodine is liberated, 
and it is stated that iodine in statii nascendi is the active germicidal 
factor. Tincture of iodine is rather widely used as a skin disinfectant 
for minor operations, for sterilizing the epidermis prior to spinal 
puncture, collecting blood for cultural purposes, and for operations 
upon laboratory animals. Iodine is absorbed through the skin, and 
in large amounts it is toxic. 
Boric Acid. —Boric acid is frequently used upon mucous surfaces and 
other exposed parts when a very mild antiseptic solution is required. 
Boric acid is rather an antiseptic than a germicide: its chief advantage 
lies in the fact that 1 to 3 per cent aqueous solutions have but little 
action on the tissues. 
All disinfectants appear to be cellular poisons to a greater or lesser 
degree; in lesser concentrations they are without marked effect upon 
1 Hamilton: Therap. Gaz., 1914, 38, 311. 
