DISINFECTION 131 
1.5 and five times as resistant as vegetative cells. The resistivity 
of some of the common bacteria is shown in Fig. 42. This author 
does not believe that hydrogen peroxide is formed during the 
action of these rays. Burge has demonstrated that these radiations 
exert a strong coagulation of the protein and probably the same 
change is secured on bacterial proteins. He declares (Burge, 1917) 
that the theory of the destruction of the intracellular enzymes to 
explain death, is not true. He killed some bacteria by ultra violet 
radiation and after grinding found that gelatin was liquefied. In this 
case the intracellular enzymes were not destroyed when the cells had: 
been killed. This same opinion was advanced by Oker-Blom (1913). 
He argues that the rays act directly on living protoplasm and do not 
act through ozone, hydrogen peroxide or nitrous acid. In this con- 
nection the greater resistance of the fluorescent bacteria to ultra violet 
rays found by Burge and Neill (1915) is interesting. They found the 
fluorescent bacteria to be much more resistant than the non-fluorescent. 
Harris and Hoyt (1917) state that visible light rays are not as a rule 
absorbed by protoplasm. Ultra violet rays are generally toxic and they 
attempted to determine what constituent of the protoplasm was 
responsible for absorption of these rays. While their experiments 
were carried out with protozoa, the results are probably applicable to 
bacteria. The paramecia were suspended in different solutions such as 
urea, cane sugar, alanin, leucine, and gelatin. They state the sus- 
ceptibility of protoplasm to ultra violet light is conditioned by the 
absorption of the toxic rays by amino acid radicles in the proteins. 
Newcomer (1917) reported that the typhoid bacilli are about 1/200 
as sensitive to ultra violet radiations of wave lengths 2100-2800 Ang- 
str6m units as a photographic plate. This decreases to almost zero 
at 2970 units. Browning and Russ (1917) working the Staphylococcus 
pyogenes aureus, B. colt and B. typhi reported that ultra violet radia- 
tions with wave lengths between 3800 and 2960 A possessed no marked 
bactericidal action. Wave lengths between 2960 and 2100 A were 
markedly bactericidal, 
DISINFECTION 
The distinction between sterilization and disinfection is quite 
artificial in many cases. In both processes the death of bacteria is 
concerned. Disinfection is generally regarded as the removal of patho- 
genic bacteria from materials while sterilization is applied to those 
processes which remove all kinds of life. Obviously all methods of 
