PRACTICAL DISINFECTION 285 
also belong to this group. The cost of such instruments is prohibi- 
tive for individual use, however, and their disinfection appears to be 
the practical solution of the problem. In hospitals the thermometers 
can be sterilized readily, first, by wiping them carefully to remove 
adherent mucus, then immersing them in 5 per cent formalin solu- 
tion,^ where they remain until wanted again. A thorough rinsing in 
water will remove the formalin. The clinician who has an extensive 
visiting practice cannot afford individual thermometers; for practical 
purposes his thermometer can be kept free from bacteria if it is washed 
each time in running water until free from mucus, and kept in a 
metallic case containing 10 per cent formalin solution prepared daily. 
Running water will remove all traces of formalin before use. At least 
two hours should be allowed before sterilization is regarded as com- 
plete. Several thermometers may be required to permit of this period 
of sterilization for each individual instrument. 
Dentists' instruments- almost without exception can be safely 
sterilized in a boiling 5 per cent solution of washing soda (sodium 
carbonate) within fi^'e minutes' exposure. If they are then wiped 
dry there is little danger of rusting. The sterilization of dental mouth 
mirrors is a problem which would appear to require special investi- 
gation. 
1 A covered container is required; the fumes of formaldehyde are very irritating to 
the patient. 
2 For details, see Hasseltine (Sterilization of Dental Instruments, Hygienic Labora- 
tory Bull. No. 101, August, 1915). 
