134 MODERN DAIRY PRACTICE. 



the origin of the ice. In examining thick lake ice in the 

 centre of a large block of ice the analyses proved it to be 

 entirely free from bacteria. On the surface of this block, 

 which was exposed to infection during the cutting, haul- 

 ing, etc., an appreciable quantity was, on the other hand, 

 found ranging from 20 to 400 per cubic centimeter. Only 

 one inch deep no bacteria was usually found ; sometimes, 

 however, a couple of bacteria colonies appeared on the 

 gelatine plates in the bacteriological analyses. The block 

 of ice was taken from the lake in March and hauled to an 

 ice-house; the analyses were made in the following August. 

 Even porous, soft ice has proved very poor in bacteria, 

 sometimes entirely sterile, if it did not come from the 

 surface layer. This was found to be the case in ice taken 

 from a lake where no city or factory was situated. The 

 results of analyses made of ice from the harbor of Helsing- 

 fors were different. They showed that the water must 

 have been very rich in bacteria before the freezing, for 

 about two months after the harbor was frozen over, the ice 

 contained between 260 and 3500 bacteria per cubic centi- 

 meter. The material for these analyses was taken by 

 myself from the ice in the harbor. No ice free from 

 bacteria was found in this place.* 



* Russell (Med. News, Aug. 17, 1889) gives bacteriological analy- 

 ses of ice from Mendota Lake (near Madison, Wis.). No factory 

 is found on the shores of this lake, but it receives a good share of 

 the sewage from about 15,000 people. The number of bacteria 

 per cubic centimeter of ice varied greatly, viz., in 62 trials from 14 

 to 1249, the average number being 270. The bacteria content of 

 the lake water varied from 3 to 3167, the average being 684 per cc. 

 About 60 per cent of the bacteria were thus lost by the freezing. 

 Prudden (Med. Eecord, 31, 344 ; see loc. cit.) claims that 90 per cent 

 are destroyed by freezing ; while Fraukel (Zeit. f. Hyg., 1, 308) has 



