238 BACTERIA 



Ice contains bacteria in varying quantities from 20 per cc. 

 to 10,000 or more. Nor is variation in number affected 

 alone by the condition of the water, for samples collected 

 from one and the same place differ widely. The quality 

 follows in large measure the standard of the water. 



Water bacteria, Bacillus colt, putrefactive bacteria, and 

 even pathogenic have been found in ice. Many of the 

 latter can live without much difficulty and are most numer- 

 ous in ice containing air-bubbles. 



Dr. Prudden, of New York, performed a series of experi- 

 ments in 1887 to show the relative behaviour of bacteria in 

 ice. Taking half a dozen species, he inoculated sterilised 

 water and reduced it to a very low temperature for a hun- 

 dred and three days, with the following results: — Bacillus 

 prodigiosus diminished from 6300 per cc. to 3000 within the 

 first four days, to 22 in thirty-seven days, and vanished 

 altogether in fifty-one days; a liquefying water bacillus, 

 numbering 800,000 per cc. at the commencement, had dis- 

 appeared in four days ; Staphylococcus pyogenes aureus and 

 B, fluorescens showed large numbers present at the end of 

 sixty-six and seventy-seven days respectively ; B. typhosus, 

 which was present 1,000,000 per cc, after eleven days, fell 

 to 72000 after TJ days, and 7,000 at the end of 103 days. 

 Anthrax bacilli are susceptible to freezing, but their spores 

 are practically unaffected (Frankland). 



From these facts it will be seen that bacteria live, but do 

 not multiply, in ice. 



In making a bacterial investigation into the flora of ice- 

 cream, it is necessary to remember that considerable dilution 

 with sterilised water is required. The usual methods of 

 examining water and milk are adopted. 



Bread forms an excellent medium for moulds, but unless 

 specially exposed the bacteria in it are few. Waldo and 

 Walsh have, however, demonstrated that baking does not 

 sterilise the interior of bread. These observers cultivated 



