24 MEDICAL BACTERIOLOGY 



the substance still remains unfit, if intended for human consumption, thera- 

 peutic administration, or for use as culture medium, upon which to grow bacteria. 



Chemical sterilization is principally employed in the treatment of refuse 

 matter which may contain pathogenic organisms. Chloroform and ether, 

 which can be removed by a slight degree of heating, are occasionally used for 

 chemical sterilization, as in the sterilization of serum. 



The rate at which chemical sterilization progresses is in proportion to the 

 hydrogen ion concentration. This consideration will explain the greater 

 activity shown by chemicals in aqueous solutions than in alcoholic or ethereal 

 admixture, since it has been shown that ionization is more pronounced and 

 greater in water than in other solutions. Sodium chloride and other chemical 

 salts when added to the solution of an inorganic disinfectant seem to retard the 

 action of the latter, inasmuch as these salts tend to decrease the concentration 

 of free ions. However, their presence with the organic disinfectants, notably 

 the phenols and coal-tar derivatives, tends to increase the bactericidal powers 

 of such preparations. This fact is sufficient proof that the phenols and their 

 allied members act as an entire molecule and not as individual ions. 



DISINFECTANTS USED IN SOLUTION 



How disinfectants effect the injury of bacteria is a problem still in doubt. 

 Some seem to act by their readiness in coagulating the cell protoplasm. Others 

 act by their power of rapidly oxidizing the bacterial body. Some may produce 

 injury to the cell by their property of withdrawing water from its tissues, while 

 still others exert their toxic effect by penetrating the cell wall and inactivating 

 the cell protoplasm. 



ACIDS AND ALKALIES 



The strong inorganic acids and alkalies are active germicidal agents, due to 

 the fact that they readily ionize. The acids possess this property to a greater 

 extent than the latter. 



Bichloride of mercury is one of the most extensively used antiseptics. 

 Although highly efficient under certain conditions, it is so readily destroyed and 

 its efficiency lowered as commonly used that it becomes an undependable dis- 

 infectant. It is poisonous, irritating and highly toxic. It is precipitated by 

 soap and its precipitating properties by albumen limits its use as a penetrating 

 agent. 



Peroxide of hydrogen has been used extensively, because of its oxidizing 

 properties. Regarded as very efficient by some, it is considered worthless by 

 others. This is because of its rapid destruction in the presence of organic 

 matter (especially blood, pus, etc.), so that no great dependence can be placed 

 upon its disinfectant properties, unless used in excessive amounts. 



Permanganate and dichromate of potash are two inorganic salts, which as 

 oxidizing agents, are powerful disinfectants. These are also rapidly reduced 

 and inactivated, as far as their bactericidal properties are concerned, by organic 

 matter. 



