152 GENERAL PHYSIOLOGY 



It has, however, no marked power of penetration, and in order 

 to be effective, all articles to be disinfected must have their 

 surfaces well exposed, and in its practical application it is a 

 point of considerable importance to see that all materials to 

 be disinfected are arranged so that the gas can readily reach 

 them. There is some difference of opinion as to the necessity 

 of moisture. It is usually stated that a considerable amount 

 of moisture is desirable, and this is probably true ; but if the 

 amount is sufficient so that it condenses on an object, it can 

 be very readily seen that it might interfere with the absorption 

 of the gas. 



The amount of formaldehyde to be used in disinfection is a 

 matter of importance. There is the same danger that not 

 enough may be used as there is in the case of sulphur. In a 

 general way one pint or pound of formaldehyde should be 

 used for every thousand cubic feet of space. 



The disadvantages, when compared with sulphur, are first 

 the cost, which is somewhat more, especially where used with 

 potassium permanganate; second, the fact that it does not 

 affect animal life, and therefore is not available for certain 

 kinds of disinfection ; and third, the strong odor which fre- 

 quently persists for some period of time. But the advan- 

 tages far offset these. The odor which persists after formal- 

 dehyde has been used may be neutralized to a considerable 

 extent by the use of ammonia. The ammonia is sprinkled 

 about the room, five parts being use4 to four parts of the for- 

 maldehyde. 



