148 DISINFECTION AND STERILIZATION 



tions as high as 1 to 2000 of the gas. It is very irritant to 

 mucous membranes of most individuals. 



Anilin Dyes.— Some of the anihn dyes show remarkable 

 selective disinfectant and antiseptic action on certain kinds 

 of bacteria with little effect on others. This has been well 

 shown by Churchman in his work on Gentian Violet. This 

 dye inhibits the growth of Gram-yositive organisms up to a 

 dilution of one part in 300,000 while on Gram-negative 

 organisms it is without effect even in saturated solution. 

 This is nicely shown in the accompanying illustration. 

 This inhibiting effect of anilin dyes is taken advantage of in 

 several methods of isolating bacteria (Chapter XVIII). 



Fig. 104. — The lower half of the plate is plain agar medium, the upper 

 half the same medium plus gentian violet to make 1 part in 300,000. The 

 Gram-positive organism is on the right and the Gram-negative on the left. 

 Streak inoculations were made across both media. 



In addition to the above-discussed disinfectants a large 

 number of substances, particularly organic, are used in 

 medicine, surgery, dentistry, etc., as more or less strong 

 antiseptics, and the list is a constantly lengthening one. 



In the laboratory chloroform, H2O2, ether and other vola- 

 tile or easily decomposable substances have been used to 

 sterilize liquids which could not be treated by heat or by 

 filtration. The agent is removed either by slow evapora- 

 tion or by exhausting the fluid with an air pump. The 

 method is not very satisfactory, nor is absolute steriliza- 

 tion easily accomplished. It is much better to secure such 

 liquids aseptically where possible. 



