XVIl] 



BACTERIOLOGY, ANTISEPTICS AND DISEASE 



203 



only water that is dangerous to drink is that' 

 which contains freshly added typhoid and other 

 pathogenic germs due to pollution from sewage, 

 etc. The presence of thousands of bacteria per 

 cubic centimetre, which is generally accepted as 

 proof of dangerous water, is no proof at all, 

 because it furnishes no evidence whatsoever of 

 the presence of pathogenic germs. In fact, 

 typhoid, cholera, and other disease microbes live 

 for only a very short while in water, and for this 

 reason a large volume of water — e.g. a large 

 river — purifies itself in its course of perhaps a 

 hundred miles. Harmful water must contain 

 colli germs or typhoid germs, as a rule. 



Most of the diseases in plants are due to 

 bacteria. The commonest are : Pear blight, wilt 

 disease (in pumpkins, cucumbers, etc.), brown 

 rot (in tomatoes, potatoes, etc.), black rot (in 

 cabbage), basal stem rot (in potatoes), and 

 yellow disease of hyacinth. All the foregoing 

 are produced by bacilli. 



798. In the following section is a list of anti- 

 septics and disinfectants. Disinfectants can be 

 used either in the blood to destroy bacteria in 

 it, as quinine, turpentine, etc. ; or in the intes- 

 tines, as salol ; or in the stomach and mouth, as 

 alcohol, ether, etc. ; or externally. This last 

 method is one adopted in aseptic surgery and in 

 the general prevention of the spread of con- 

 tagious diseases, and is the one that concerns us 

 most here. 



The term "antiseptic" really refers to those 

 agents that prevent the growth of micro-organ- 

 isms, but it is frequently used in the same 

 sense as the term disinfectant. The term 

 "disinfectant" refers to those agents that 

 actually destroy microbes. It is clear, therefore, 

 that only the more powerful of antiseptics are 

 really disinfectants, i.e. a disinfectant must also 

 be an antiseptic, but an antiseptic is not neces- 

 sarily a disinfectant. 



If an infected substance is acted upon by a 

 true antiseptic, the microbes are prevented from 

 growing, and in time will die (with the excep- 

 tion of anthrax and tetanus bacilli). The period 

 during which they will live depends on their 

 surroundings ; therefore, if they are exposed to 

 healthy surroundings, they may only live a few 

 hours. 



Antiseptics 



799. (Those marked (d) are disinfectants as 

 well. Those disinfectants specially recommended 

 as being quite safe and reliable under most con- 

 ditions are printed in capital letters.) 



Practically all disease-producing microbes 

 are destroyed if boiled in water at atmospheric 

 pressure (bar. 30 in.) for three minutes. This 

 process, known as sterilisation, is the surest 

 method of making instruments and vessels 

 aseptic, because it is difficult to be sure that 



