4 
consists of a solution of the isomeric forms of formaldehyd, especially 
paraformaldehyd. 
Formalin solutions are unstable. In cold weather they are apt to ■ 
precipitate a white substance, usually trioxymethylen. Heating and 
evaporating them has a tendency to change the formaldehyd to paraform. 
These facts are stated to emphasize the importance of not considering 
commercial ‘Hormalin*’ as a simple solution of a gas in water. This 
has no bearing in using formalin as a liquid disinfectant in the same 
way that we would use solutions of bichloride of mercury or carbolic 
acid, but it has a very distinct and important bearing in gaseous disin- 
fection with formaldehyd. 
It is not the scope of the present article to dwell upon the best way 
to obtain the gas formaldehyd from its solution. The present work 
points out the difficulty of obtaining the gas without special apparatus 
from its solution in a closed container. 
The power of formaldehyd. gas as a disinfectant depends on the 
chemical change which takes place between the gas and the albuminous 
matter of the germ. To be effective, therefore, the gas must not only 
be brought in direct contact with the germ, but in sufficient amount 
and for a sufficient length of time. In this respect it does not differ 
from bichloride of mercury and other chemical disinfectants. This 
point is especially mentioned here on account of the difficulty of obtain 
ing formaldehyd gas in its free state, and the uncertainty as to the 
amount of gas evolved from its solution, important factors which must 
be taken into account in practical disinfection. 
Formaldehyd forms a chemical compound with albuminous matter 
from which it is impossible to again separate it. It renders gelatin 
insoluble when added in small amounts. Egg albumen, to which 
formalin has been added, can not be coagulated by heat. This prop- 
erty of ‘ffixing^’ organic matter makes it valuable as a re-agent, in 
microscopy and explains some of its limitations as a disinfectant. 
Jtlethods. 
Young bouillon cultures of typhoid and diphtheria, one to two days 
old, and older cultures of authrax, containing spores, were used to 
impregnate slips of paper. 
TThite filter paper is cut into slips about 1 inch long, by one- fourth of 
an inch wide and sterilized by dry heat. These are convenient to drop 
into test tubes. The slips are impregnated with the bouillon cultures 
and exposed between the blankets and sheets in the boxes. 
Freshly prepared, moist slips were used throughout this work, 
because moist cultures are more readily killed by formaldehyd than 
dry ones, and it was designed throughout to make the conditions favor- 
able for the disinfecting action^ of the gas to act. 
The blankets and sheets used in these experiments are folded to fit 
the boxes and then sterilized with steam. The slips of paper contain- 
