THE COMBINED METHOD OF STERILISATION 91 



constitute the rule), its favourable action in the healing of wounds is based 

 exclusively on the counteraction of the poison produced by the pus-forming 

 bacteria, without, however, the appearance of the latter being prevented. The 

 use of chloroform for disinfection is only, as a rule, resorted to when it is desired 

 to sterilise milk for use as a culture medium, in which case it is necessary to 

 dispense with strong heat. This will be discussed in a subsequent chapter. 



The organic acids have a fatal effect, even in small quantities, especially on 

 putrefactive bacteria. Frequent and regular use is made of this property in 

 technical processes of sterilisation, as also in distillery work ("souring the 

 mash "), as will be frequently noticed in the course of the present work. On 

 the other hand, fairly high degrees of concentration are required for killing such 

 bacteria as are themselves active producers of acid. Benzole acid, though pro- 

 hibited by law, is occasionally employed for increasing the keeping properties of 

 milk. This acid even in very small quantities has a very restrictive influence 

 on alcoholic fermentation, and it is to this influence that the difficulty of 

 exciting fermentation in the juice of the whortleberry (Vaccinium Vitis Idcea) 

 is to be ascribed, considerable quantities of this acid being present therein, MAOH 

 and POKTELE (I.) having found 0.64 to 0.86 grm. per litre. 



81. The Combined Method of Sterilisation. 



The influence exerted on micro-organisms by the substances already con- 

 sidered is subject to the same fundamental law as has been established for 

 physical force, viz., that the effect produced varies with the intensity of the 

 causative influence. A solution containing so large a proportion of antiseptic 

 that it is capable of killing a given microbe, will, when sufficiently diluted, have 

 a merely restrictive influence on development, without, however, proving fatal. 

 Proceeding farther in the same direction, a condition of dilution will be 

 attained which will exert a favourable effect, stimulating the vital activity of 

 the organism ; and finally, if the degree of dilution be extended beyond this 

 point, no effect will be observable. This fact was expressed by HUGO SCHULZ (I.) 

 in the following phrase: "Each impulse exerts on each cell an action whose 

 effect on the activity of the cell is in inverse proportion to the intensity of the 

 impulse." A series of researches, which confirm this law, have been made on 

 microbe poisons, but it will be sufficient to simply mention two examples, viz., 

 that of CH. RICHET (I.), treating of the bacteria of lactic fermentation, and that 

 of BIERNACKI (I.), which deals with alcoholic fermentation. 



This law forms the basis of the theory of toxic action originated by O. Low(IL) 

 in a book the perusal of which is commended to the reader, and more especially 

 for the complete critical digest it contains of the literature, relating to the action 

 of poisons, published anterior to 1893. According to Low, the ultimate cause 

 of toxicity is to be sought in the lability of the albuminoid matter of the cell 

 protoplasm. The activity of the latter consists in a continuous chemical change 

 of the atomic groups composing the molecule, the briskness of which alteration 

 is increased by slight stimuli. Larger quantities of the irritant (poison) exert 

 such a strong preponderating influence on the change, that the lability of the 

 plasmic albuminoid is arrested, and the life of the cell is consequently destroyed. 

 Probably, then, toxic action may be the means of throwing light upon the obscure 

 problem of the chemical dynamics of the cell ; just as, in many other branches 

 of natural philosophy, the study of disturbing influences has afforded the deepest 

 insight into the normal course of phenomena. 



A knowledge of the nature of toxic action the progress of which depends 

 more or less upon chemists obtaining a clear idea as to the constituents of the 

 albuminoids is of the greatest importance, both to the study of organic life in 



