162 BACTERIOLOGY. 
dehyde also forms combinations with certain aniline 
colors—viz., fuchsin and safranin—the shades of which 
are thereby changed or intensified. These are the only 
colors, however, which are thus affected, and as they 
are seldom used in dyeing, owing to their liability to 
fade, this effect is of little practical significance. The 
most delicate fabrics of silk, wool, cotton, fur, leather 
ete., are unaffected in texture or color by formaldehyde. 
Iron and steel are attacked, after long exposure, by the 
gas, and more so by its solution; but copper, brass, 
nickel, zine, silver, and gilt work are not at all acted 
upon. Formaldehyde unites with nitrogenous products 
of decay —fermentation or decomposition—forming true 
chemical compounds, which are odorless and sterile. It 
is thus a true deodorizer in that it does not replace one 
odor by another more powerful, but forms new chemical 
compounds which are odorless. Formaldehyde has a 
peculiar action upon albumin, which it transforms into 
an insoluble and indecomposable substance. It ren- 
ders gelatin insoluble in boiling water and most acids 
and alkalies. It is from this property of combining 
chemically with the albuminoids forming the protoplasm 
of bacteria that formaldehyde is supposed to derive its 
bactericidal powers. Formaldehyde is an excellent pre- 
servative of organic products. It has been proposed to 
make use of this action for the preservation of meat, 
milk, and other food products; but, according to Trillat 
and other investigators, formaldehyde renders these sub-. 
stances indigestible and unfit for food. It has been 
successfully employed, however, as a preservative of 
pathological and histological specimens. 
There are no exact experiments recorded of the 
physiological action of formaldehyde on the human 
