GENERAL BACTERIOLOGY 
35 
or destroyed by sunlight, although marked variation ex¬ 
ists among different bacteria as regards this. 
Electricity. —Electric light exerts a distinct bacterici¬ 
dal (bacteria killing) effect when applied in the strength 
of 800 to 900 candle power for six to nine hours. Koentgen 
or x-rays do not seem to have any bactericidal effect, 
while radium has both an inhibitory and bactericidal effect 
when applied at a distance of a few centimeters for a few 
hours. 
XII. The Biological Activities of Bacteria 
While the pathogenic, or disease-producing, properties 
are of immediate interest to us, we must not lose sight 
of the fact that these properties are merely a side action, 
so to speak, compared with other numerous bacterial 
activities, and that the pathogenic bacteria are the least 
numerous group of all the bacterial clans. The pro¬ 
duction of disease is merely incidental to the success¬ 
ful attempt on the part of the bacteria to establish a 
new domicile in the human or animal body. 
The much more important functions of the bacteria 
are those with which they serve the many important 
and useful purposes in the world’s economy. 
It is absolutely no exaggeration to say that without 
bacteria all reduction of complex organic matter to 
simple compounds and the chemical interchange be¬ 
tween the animal and the vegetable kingdoms could 
not be carried out and all life on earth would cease, 
as Hiss and Zinsser so well say (Textbook of Bacteriology 
1914, p. 41) : “Far from being scourges, these minute 
microorganisms are paramount factors in the great 
cycle of living matter.” 
The Katabolic (Breaking Down) Activities of Bac¬ 
teria. —The katabolic activities of bacteria consist in 
