BY DR. 0. KATZ. 257 



So also did G. Bordoni-Uffreduzzi* with reference to the natural 

 ice used in Turin. 



On the other hand, the labours of these three investigators 

 resulted in showing that, by the process of freezing, the water rids 

 itself to a large extent from the living bacterial material originally 

 in it. Frankel, as the first, pointed out (I.e.) that the power of 

 bacteria to resist a great cold was only a limited one, so much so 

 that the ice always contained much fewer bacteria than the original 

 water, that therefore, even water containing a good many microbes 

 may furnish a tolerably good ice. Hence ice rich in bacteria must 

 be looked upon as coming from a very impure water, and in such 

 a case a certain precaution in using it is indicated. 



Prudden (I.e.) and Bordoni-TJffreduzzi (I.e.), both arrived at the 

 conclusion that by moderately prolonged freezing, about nine- 

 tenths of the water-bacteria are killed, so that only a small 

 fraction (one-tenth) remain alive. 



Prudden (I.e.) undertook also a series of experiments with the 

 view of ascertaining how a limited number of known microbes — 

 pathogenic and non-pathogenic ones — behaved themselves when 

 exposed (in sterilised water) to the effects of an artificially pro- 

 duced cold, as far as - 24°C., for a period up to 103 days. He 

 obtained the remarkable result that pathogenic species withstood 

 such an excessive cold much longer than non-pathogenic ones. 

 While, for instance, Micrococcus prodigiosus, showing before 

 freezing 6300 colonies in 1 ccm., was killed after 51 days' unin- 

 terrupted freezing ; a liquefying bacillus from water, with at 

 first 800,000 in 1 ccm., after 4 days; Staphylococcus pyogenes 

 aureus derived from a vigorous culture, with innumerable germs 

 in 1 ccm. of water at the commencement, still contained 50,000 

 living individuals after G6 days ; and the bacillus of typhoid 

 fever, showing after 11 days one million germs, 7000 colonies in 

 1 ccm. after 103 days. On the other hand, an alternate freezing 



*" Die Ijiologische Untersuchung des Eises in .seiner Beziehnng zur 

 iiffentlichen (Jesunflheitspllege " Centralbl. f. Bakteriologie nnd Parasiteu- 

 kunde, Bd. II., No. 17, 1887, pp. 489-4'J7, 

 17 



