634 A MANUAL OF BACTERIOLOGY 



that the soaps owe such power as they possess against 

 naked organisms. The relative efficiency of soaps in 

 practical disinfection may be understated by the results 

 of comparative experiment on laboratory cultures because 

 the resistance of the microbe itself to disinfection by 

 chemical substances, and, indeed, by other agencies, may 

 be small compared with the resistance offered by the 

 envelope of grease or greasy dirt, derived from perspiration, 

 pus, fat, and the oily grime which pervades cities and is 

 everywhere caused by handling. A disinfectant of greater 

 efficiency than soap on a laboratory culture may, therefore, 

 be of much less efficiency on an infection in actual practice. 

 Soaps are incompatible with most disinfectant substances, 

 but not with all. Biniodide of mercury can be prepared 

 with soap, and for surgical purposes is a disinfectant of 

 high value. The " carbolic soaps " of commerce are, for 

 the most part, worthless. 



Caustic lime, used generally as a 20 per cent, milk, has 

 considerable disinfectant power, and has been applied to 

 the disinfection of fseces. For this purpose care has to 

 be taken to break up any lumps of excreta, and whenever 

 practicable a heat process, of which the efficiency and 

 rapidity may be greatly increased by an alkaline disinfec- 

 tant, is much to be preferred. Lime is inefficient against 

 the more resistant organisms, and lime-washing cannot 

 be considered a sufficient precaution against them or 

 against infections, such as those of scarlet fever and small- 

 pox, of which the exciting organism is unknown. 



Halogens. The disinfectant values of dry chlorine, 

 iodine, and bromine are low. Both in a dry and a damp 

 state chlorine is inconvenient, and the others are costly ; 

 and the use of halogens is therefore practically confined 

 to solutions, notably " chloride of lime " (a mixture of 

 calcium hypochlorite, hydrate, and chloride) and hypo- 

 chlorite of soda (chloros). These have a powerful effect on 



