MECHANISM OF DEATH 345 



have learned to eliminate some errors, such as using distilled water 

 of unknown pH, or producing heat shocks and cold shocks, the 

 variation of parallel experiments on different days is still very great. 

 The only certain way to get uniform data is to prepare a large number 

 of bacteria in a uniform way, and preserve them for later experi- 

 mentation. This was done by Paul (1910) in drying a Micrococcus 

 suspension on garnets, and by Myers (1929) in keeping a suspension 

 of bacterial spores frozen. Both these authors obtained comparable 

 data over long periods of time. 



The old type of disinfection experiments by the endpoint method 

 suffers naturally from the same irregularities, but since the results 

 are not as precise as in plate count experiments, the variation is not 

 so obvious. It is not logical, therefore, to reject data and findings 

 obtained by the newer methods, because their more accurate measure- 

 ments reveals plainly a great variability of the microorganisms while 

 the cruder endpoint method does not show this so distinctly. 



Very little attention has been paid so far to the 

 specificity of the different species. It is to be expected 

 that among unicellular organisms, differences in resist- 

 ance will be much greater than among multicellular 

 organisms. This is evidenced by bacteria capable of 

 feeding on formaldehyde (Kaserer, 1906), xylol (Soehn- 

 gen, 1906), metabolizing arsenic {Penicillium brevicaule), 

 or living at pH 1 (Waksman's sulfur bacteria, 1922). 



A first step in this direction is the observation of 

 Cooper and Mason (1927, 28) that the Pseudomonas 

 group (Ps. fluorescenSy Ps. non-liquefaciens and Ps. 

 pyocyanea) is quite sensitive to ^'physico-chemical" 

 reagents causing precipitates of proteins, such as alcohol 

 or phenol, while Bad. coli is less sensitive to these com- 

 pounds, but reacts strongly with ''chemical" disin- 

 fectants such as quinones. 



The Pseudomonas group which is sensitive to precipi- 

 tants is also much more sensitive to heat; this suggests 

 that the colloidal state of their protoplasm is different 

 from that of the colon group. 



