STERILIZATION ANTISEPSIS FOOD PRESERVATION 71 



they may fail to sterilize even in case of such materials, es- 

 pecially in the presence of rapidly growing spore-producing bac- 

 teria and when there are spores of anaerobic bacteria in the 

 material to be sterilized. On this account, materials sterilized 

 in this way should not be injected into patients. 



Electricity has little or no direct demonstrable germicidal ac- 

 tion. An electric current may generate sufficient heat to kill 

 bacteria, or it may produce powerful germicides by electrolysis, 

 such for example as acids and alkalies. 



Chemical Agents, Sterilization by means of chemicals is 

 not employed in the preparation of culture media because of the 

 difficulty of removing the added substance after the desired effect 

 has been obtained. It is necessary in every case to consider 

 the other effects which the use of chemical germicides entails, and 

 their usefulness is therefore somewhat more limited than that of 

 the physical agents for sterilization. Their efficiency is also 

 subject to great variation according to the nature of the materials 

 with which they come in contact. Nevertheless they have a 

 very important place in practical sterilization and disinfection. 



The common soaps, and more particularly green soap, have 

 a slight germicidal value, and this in conjunction with their sol- 

 vent action upon fats and protein, and the mechanical cleans- 

 ing which accompanies their use, justifies assigning them an 

 important place among the chemical disinfectants. 



Acids, especially those which are strongly dissociated, are 

 powerful germicides. Hydrochloric acid apparently owes its 

 power entirely to its acidity, and in fairly weak solution, 0.2 to 

 i .o per cent, it kills vegetative bacteria in a short time. Strong 

 sulphuric acid actually carbonizes organic matter, while nitric 

 acid oxidizes and also forms special combinations with protein, 

 the reactions resulting in death of living protoplasm. Sulphurous 

 acid (sulphur dioxide) also possesses marked germicidal proper- 

 ties, probably due to oxidation effects. 



Sulphur dioxide gas has been employed extensively in the 

 fumigation of rooms, and is usually prepared by burning sulphur. 



