150 GENERAL PHYSIOLOGY 



is added in a small amount, namely 10 per cent, that poly- 

 merization is prevented. 



There are a number of pieces of apparatus on the market, 

 sold at a very reasonable price, which do excellent service as 

 regenerators. Among the lower-priced ones, those having a 

 copper retort, heated by a Primus lamp, are probably the most 

 satisfactory. They are so arranged that they can be run out- 

 side of the space to be disinfected. The gas produced by 

 them is led into the apartment through a keyhole or other 

 small opening. In this way the operator has the apparatus 

 under his control during the entire operation. The gas can 

 also be regenerated from the paraformaldehyde, or the solid 

 form. In this case the white material, which is put up under 

 different names, is heated over a flame and broken up into 

 the gas. The gas maybe regenerated also from the solution 

 when the latter is sprayed in very fine drops on a large surface. 

 If the drops are small and sufficiently separated from one 

 another, so that they do not run together and hence 

 evaporate rapidly, little polymerization takes place. These 

 principles are at the basis of what is known as the 

 Chicago Board of Health method of formaldehyde disinfection. 

 This method is useful at times, but the difficulty comes, under 

 ordinary conditions, in getting enough formaldehyde sprayed 

 on to the sheets which are used to produce satisfactory disin- 

 fection before it is necessary for the operator to leave the room. 

 In many ways the most satisfactory method of regenerating the 

 gas is to bring it in contact with some chemical substance with 



