142 STERILIZATION AND DISINFECTION 
enzymological work. It is used in many pharmaceutical preparations 
but probably does no harm. 
CH(CHa)2 
Formaldehyde. This is a powerful disinfectant sold in 35 per cent 
solutions under the name of formalin. Formaldehyde changes to para- 
formaldehyde by polymerization when kept at room temperatures. It 
unites easily with many substances especially the organic compounds. 
For instance when added to gelatin it forms a compound which is 
insoluble in many of the common reagents. Fermi attempted to secure 
a gelatin medium in this way which would not melt at room tem- 
perature. It may act in the same way on bacterial protein. It is 
important to have plenty of moisture present when using formaldehyde 
as a disinfectant. Koch (1901) reported that a 0.05 per cent solution 
of this compound would kill growing yeast while a 0.005 per cent solu- 
tion would not. Since carbon dioxide was formed after the cell had 
been killed, the zymase was not destroyed. 
Glycerol. Rosenau has made an interesting study of this com- 
pound in its relation to dinsinfection. He found that a 50 per cent 
solution of glycerol would restrain all bacterial growth and that lower 
precentages would allow better growth. Bacteria would not grow 
in media containing 32 per cent of glycerol but molds grew in stronger 
solutions of 40 and 49 per cent. Glycerol was found to have a distinct 
but slight germicidal action and probably acted by virtue of its abstract- 
ing water from the bacterial cell. Spores were not killed and anthrax 
spores lived 200 days in strong glycerol solutions. The compound 
may be used by many bacteria as a food. It is then probably oxidized 
to glyceric aldehyde and glyceric acid. Glycerol may be used, however, 
as a carrier for many other disinfectants such as phenol, cresol, ete. 
Goodrich (1917), however, has shown that glycerol more or less com- 
pletely destroys the antiseptic power of thymol, phenol, boric acid, and 
mercuric chloride in aqueous solution. Ruediger (1914) found a 
distinct but weak bactericidal action of glycerol which was stronger 
at 30°-than at 15°C. The action is limited by the diluent. Glycerol 
diluted with normal salt solution killed bacteria more quickly than 
when diluted with bouillon. In dilutions of 50 per cent anthrax 
