ALKALIES AND HALOGENS 763 



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 infec- 

 tion in actual practice. Soaps are incompatible with 

 most disinfectant substances, but not with all. Binio- 

 dide 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 faeces. 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 dis- 

 infectant, 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 laboratory cultures, but in practice need to be used in 

 excess proportionate to the amount of organic matter 

 which may be present. Thus, for instance, a 1 per cent, 

 solution of hypochlorite of soda mixed with an equal 

 volume of urine loses the whole of its available chlorine 

 almost immediately, and becomes inert as a germicide. 

 Where the amount of organic matter is small, and the 



