276 BACTERIA IN OTHER FOODS 



Laboratory experiments have confirmed the conclusion that 

 a freezing process is not necessarily fatal to bacterial life 

 (see p. 18). We have instances of bacteria multiplying at zero, 

 and of their survival after six months' exposure to the temperature 

 of liquid air. It would appear that about 90 per cent, of the 

 ordinary water bacteria are eliminated by the process of freezing. 

 In the case of a specific pathogenic organism such as the 

 B. typhosus, less than 1 per cent, survive simple freezing for a 

 period of fourteen days. Complete sterility does not occur even 

 at the end of three months, whilst a process of alternate thawing 

 and freezing, if on the whole more fatal to the typhoid germs 

 than a simple freezing, is equally unsuccessful in effecting an 

 absolute sterilisation of the infected water. The reduction in 

 the number of typhoid bacilli in chilled water is approximately 

 as great as occurs in ice. Cold exercises an inhibitory action 

 as regards the typhoid bacillus, and in natural ice there is a 

 supplementary purifying influence to be taken into account, as, at 

 the time of freezing, 90 per cent, of the germs are thrown out by a 

 process of physical exclusion. Therefore, the danger of infection in 

 the case of ice, if it is minimised, is not abolished. A certain number 

 of typhoid bacilli do remain alive, and these may, on rethawing, 

 undergo a rapid multiplication outside as well as inside the human 

 body. And it has likewise to be remembered that it is notoriously 

 difficult to trace the exact channels of infection in sporadic cases of 

 typhoid fever. Sedgwick and Winslow have rightly drawn attention 

 to the unfavourable conditions furnished by natural ice for the 

 propagation of the typhoid organism. 



In making a bacterial investigation into the flora of ice and 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. 



4. Bread 



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 numerous bacteria 

 from the centre of newly-baked London loaves.* The writer has 

 recently made a series of examinations of the air of some nine or ten 

 underground bakehouses in central London. The general result of 

 these investigations was that the air of the typical underground 

 bakehouses examined — (1) contained 14-8 volumes per 10,000 of 

 carbonic acid gas, COg (as compared with 4-9 in above-ground bake- 

 houses, and 4-3 in the street) ; (2) that it contained between 10 and 

 * Brit. Med. Jom:, 1895, vol. ii., p. 519. 



