166 ANTISEPTICS 



stages of the purification process, large amounts of free nitrogen 

 come off the bed, but whether at such periods anaerobic bacteria 

 are or are not in the ascendant, is not known. It is probable 

 that, from the practical standpoint, the later stages of purification 

 should take place with free oxidation, as when anaerobic bacteria 

 are active at this point a very offensive effluent is produced. 



Often the effluent from a sewage purification system contains 

 as many bacteria as the sewage entering, but there is often a 

 marked diminution. It is said by some that pathogenic 

 bacteria do not live in sewage. The typhoid bacillus has been 

 found to die out when placed in sewage, but it certainly can 

 live in this fluid for a much longer period than that embraced 

 by any purification method. Thus the constant presence of 

 b. coli, b. enteritidis, and streptococci which has been observed 

 in sewage effluents must here still be looked on as indicating a 

 possible infection with the typhoid bacillus, and it is only by 

 great dilution and prolonged exposure to the conditions present 

 in running water that such an effluent can become suitable for 

 forming a part of a potable water. 



ANTISEPTICS. 



The death of bacteria is judged of by the fact that, when 

 they are placed on a suitable food medium, no development 

 takes place. Microscopically it would be observed that division 

 no longer occurred, and that in the case of motile species move- 

 ment would have ceased, but such an observation has only 

 scientific interest. From the importance of being able to kill 

 bacteria, an enormous amount of work has been done in the way 

 of investigating the means of doing so by chemical means, and 

 the bodies having such a capacity are called antiseptics. It is 

 now known that the activity of these agents is limited to the 

 killing of bacteria outside the animal body, but still even this is 

 of high importance. 



Methods. These vary very much. In early inquiries a great point 

 was made of the prevention of putrefaction, and work was done in the 

 way of finding how much of an agent must be added to a given solution 

 such as beef extract, urine, etc., in order that the bacteria accidentally 

 present might not develop ; but as bacteria vary in their powers of re- 

 sistance, the method was unsatisfactory, and now an antiseptic is usually 

 judged of by its effects on pure cultures of definite pathogenic microbes, 

 and in the case of a sporing bacterium, the effect on both the vegetative 

 and spore forms is investigated. The organisms most used are the 

 staphylococcus pyogenes, streptococcus pyogenes, and the organisms of 

 typhoid, cholera, diphtheria, and anthrax the latter being most used 



