452 Dr. Allan Macfadycn [June 8, 



trum, at the red end there is little or no germicidal action. It is 

 evident that the continuous daily action of the sun along with desic- 

 cation are important physical agents in arresting the further develop- 

 ment of the disease germs that are expelled from the body. 



It has been shown that sunlight has an important effect in the 

 spontaneous purification of rivers. It is a well-known fact that a 

 river, despite contamination at a given point, may show little or no 

 evidence of this contamination at a point further down in its course. 

 Buchner added to water 100,000 colon bacilli per cubic centimetre, 

 and found that all were dead after one hour's exposure to sunlight. 

 He also found, that in a clear lake the bactericidal action of sunlight 

 extended to a depth of about six feet. (Sunlight must therefore be 

 taken into account as an agent in the purification of waters, in ad- 

 dition to sedimentation, oxidation and the action of algae. 



Air or the oxygen it contains has important and opposite effects on 

 the life of bacteria. In 1861, Pasteur described an organism in con- 

 nection with the butyric acid fermentation which would only grow in 

 the absence of free oxygen. And since then a number of bacteria, 

 showing a like property, have been isolated and described. They 

 are termed anaerobic bacteria as their growth is hindered or stopped 

 in the presence of air. The majority of the bacteria, however, are 

 aerobic organisms inasmuch as their growth is dependent upon a free 

 supply of oxygen. There is likewise an intermediate group of 

 organisms, which show an adaptability to either of these conditions, 

 being able to develop with or without free access to oxygen. Pre- 

 eminent types of this group are to be met with in the digestive tract 

 of animals, and the majority of disease-producing bacteria belong to 

 this adaptive class. When a pignient-producing organism is grown 

 without free oxygen its pigment production is almost always stopped. 

 For anaerobic forms IS and H 2 give the best atmosphere for their 

 growth, whilst C0 2 is not favourable and may be positively injurious," 

 as e.g. in the case of the cholera organism. 



The physical conditions favouring the presence and multiplica- 

 tion of bacteria in water under natural conditions are a low altitude, 

 warmth, abundance of organic matter and a sluggish or staguant 

 condition of the water. As regards water-borne infectious diseases 

 such as typhoid or cholera, their transmission to man by water may 

 be excluded by simple boiling or by an adequate filtration. The 

 freezing of water, whilst stopping the further multiplication of 

 organisms, may conserve the life of disease germs by eliminating the 

 destructive action of commoner competitive forms. Thus the typhoid 

 bacillus may remain frozen in ice for some months without injury. 

 Employment of ordinary cold is not therefore a protection against 

 dangerous disease germs. 



As regards electricity, there is little or no evidence of its direct 

 action on bacterial, life, the effects produced appear to be of an 

 indirect character due to the development of heat or to the products of 

 electrolysis. 



