DISINFECTION AND DISINFECTANTS. 163 



which may be present. Circulation is strictly speaking a means of cleansing. 



Purification of flowing water, as rivers and small streams, is effected 

 very largely by oxidation and dilution. The agitated water takes up oxygen 

 by absorption which combines with the organic particles suspended in the 

 water rendering it unsuitable as food for bacteria. As the water flows along 

 the bacteria are scattered more and more. Sedimentation is also an im- 

 portant factor in the destruction of bacteria. Gradually the bacteria settle 

 to the bottom of the stream where they are brought in competition with 

 other bacteria, protozoa, algae, perhaps hyphal fungi, etc., which tend to 

 check and even entirely inhibit their further development. 



H. Light. — Sunlight has most marked germicidal powers, due in part, 

 to the drying effects produced and in part to the actinic or chemically active 

 rays of the sun's light. Numerous investigators have demonstrated the 

 germ-destroying effects of the blue and violet- rays and the ultra violet end of 

 the solar spectrum. Bacteria cannot survive in sunlight. Electric light is 

 said to have the same effect upon bacterial life as sunlight. The X-rays 

 destroy bacteria, likewise does radium, and these agents have been extensively 

 tested ia the treatment of skin diseases and superficial tuberculosis as lupus, 

 and in cancer, but without satisfactory or conclusive results. The germ- 

 destroying effects of sunlight are not due to heat as may be shown by the 

 use of an alumn tank which intercepts the heat rays. 



I. Electricity. — The electrical current in itself appears to be without 

 germicidal powers, but electricity is used to precipitate smelter fumes, and 

 organic impurities in water, as already stated. Electricity is used to stimu- 

 late seed germination and it may be possible to utilize electrical discharges 

 or currents in the treatment of communicable diseases. 



2. Chemical Disinfectants. 



Chemical disinfectants may be divided into gaseous (or vaporous) and 

 liquid (solutions). The liquid disinfectants are superior to the gaseous 

 disinfectants because direct contact with the articles to be disinfected can be 

 brought about, as in washing, immersing or mixing. Gaseous disinfectants 

 are effective for surface sterilization, especially useful for inaccessible rooms, 

 buildings, ships, paintings, books, fabric, etc. Both have their special 

 advantages, however. 



The number of chemical disinfectants, variously classed as gaseous, 

 liquid, patent, proprietary, efficient, useful, useless, etc., etc., is very great. 

 We shall mention only a few of the more powerful kinds. No reliance 

 should be placed in any patented or proprietary disinfectant until its value has 

 been demonstrated by tests made by reliable bacteriologists, giving its phenol 

 coefficient. Nor is this all, not only must the disinfectant have actual germ- 



