74 MICROBIOLOGY 



2.5 per cent solution in water can be obtained. It is consid- 

 ered to be less poisonous than carbolic acid and about three 

 times as powerful as a disinfectant. It seems to. be the most 

 efficient of the cresols. It is usually employed in about a one 

 per cent solution. It is much more rapidly destructive to 

 spores than carbolic acid. The cresols are not very soluble in 

 water. Harrington states that creolin (contains 10% cresols 

 and a small quantity of carbolic acid) , and lysol 

 (contains 50% cresols with neutral potash soap) are very 

 efficient as disinfectants. There are many other preparations, 

 containing cresols that are on the market and recommended as 

 disinfectants. 



Calcium compounds. The use of lime was early resorted 

 to as a disinfectant. The milk of lime and lime water are the 

 most valuable forms. 



Milk of lime is prepared by adding 1 quart of freshly 

 slacked lime to from 4 to 5 quarts of water. Air slacked lime 

 is of little or no value as a disinfectant. When surfaces are 

 thoroughly covered and brushed with this mixture most of 

 the bacteria are destroyed. If it does not kill them outright 

 it imprisons them so that they perish. It is much used for 

 disinfecting stables and pens. Lime water is a very good dis- 

 infectant for non spore-bearing bacteria. 



Chlorinated lime, which is prepared by passing nascent 

 chlorin gas over moist calcium hydrate, should contain not less 

 than 35% of available chlorin. It is prepared for use by mix- 

 ing 6 oz. of the lime with a gallon of water. It is frequently 

 applied as a dry powder for the disinfection of excreta, yards,, 

 etc. It is also a powerful deodorant. 



Formalin. When applied in solution one part of for- 

 malin to ten parts of water is- used. This is equal in its disin- 

 fecting powers to a 5% solution carbolic acid (phenol). On ac- 

 count of its irritating effect it is rarely used in solution but it 

 is applied as a gas. 



Formaldehyde gas. This is the most widely used gen- 

 eral disinfectant. It can not, however, be used unless the room 

 to be disinfected can be sealed tight. For this reason it is of 



