26 MICRO-ORGANISMS AND FERMENTATION. 



extend over a considerable period, as it often proves to be the 

 case that the cells have not been killed, and after a considerable 

 time they may germinate again. The degree of dilution at which 

 an antiseptic operates restrictively on species is usually depend- 

 ent on whether the action takes place in a nutritive fluid or not. 

 In the first case, the chemical nature of the liquid obviously 

 has considerable influence. Thus, for instance, liquids which 

 are rich in albuminoids weaken the effect of many poisons. 

 In a determination of this character for industrial purposes it 

 is usual to limit the solvent to some particular fluid. 



As an example of the part that the solvent plays, the 

 classical work of Koch in 1881 may be mentioned, which led 

 to the proof that many antiseptics may wholly or partly lose 

 their power according to whether they are dissolved in water, 

 in ethyl or methyl alcohol, ether, or acetone. In this connec- 

 tion an important fact may be noted. The addition of sodium 

 chloride to certain antiseptics (e.g., to carbolic acid or mercuric 

 nitrate solution) causes an extraordinary increase in their 

 antiseptic power. 



Temperature, also, has an influence on their action ; the 

 higher the temperature, the greater their activity. On the 

 other hand, a dilute antiseptic exhibits the least restrictive 

 power at that temperature which is most favourable to the 

 organism. 



Numerous investigations regarding the influence of antisep- 

 tics on different species of micro-organisms have shown that 

 no general rule can be traced. One species may be much more 

 resistant to one poison than many other species, whereas it 

 may exhibit little resistance to another poison. The destruc 

 tiveness of a given substance cannot, therefore, be defined in 

 general, but only its behaviour towards a particular species. 



The application of antiseptics for the cleansing of vessels, 

 etc., must always be preceded by a thorough mechanical 

 cleaning. 



Antiseptic substances are partly inorganic, partly organic. 

 Amongst the mineral substances, the first place must be given 

 to mercuric chloride, on account of its extremely poisonous 

 character. It is used in the laboratory in a solution of 

 1 gramme per litre of water, but it is impossible to use it in 



