408 PRESERVATION OF FOOD 



Salt is extensively used in the preservation of meats and pickles, 

 and our knowledge concerning the action of salt is more exact than 

 it is concerning sugar. 



Tanner lists the various reasons which have been ascribed for the 

 keeping powers of salt as f ollow r s : 



I. Exerts a poisonous action. 



II. Renders the moisture unavailable for microorganisms. 



III. Destroys the cells by plasmolysis. 



Salt does not render the medium sterile but exerts a selective 

 action upon the bacterial flora. A -7 to 10 per cent, solution of salt, 

 according to Stadler, inhibited the growth of the following organisms : 

 B. Coli commune, B. morbificdus boms, B. enteriditis, B. (proteus) 

 vulgaris, and B. botulinus. 



De Freytag and Stadler found that a saturated salt solution had 

 the following effect upon bacteria : 



INFLUENCE OF CONCENTRATED SALT SOLUTION ON BACTERIA. 



Author. Organism. Observation. 



Freytag . . . B. anthracis Not killed after a number of hours. 



Freytag B. anthracis spores Not killed in six months. 



Freytag . . . B. typhosus Killed after five months. 



Stadler .... B. typhosus Not killed in six weeks. 



Freytag . . . B. diphtherice . Not killed in three weeks. 



Stadler .... B. diphtherice Not killed in four and a half weeks. 



Freytag B. tuberculosis Not killed in three months. 



Stadler .... B. pestis Not killed in sixteen weeks. 



Homer found that B. botulinus does not develop in media con- 

 taining over 6 per cent, of salt, and he considers meat which is 

 properly covered with brine safe. But much higher concentrations 

 12 to 19 per cent, acting for seventy-five days are necessary to 

 destroy the bacteria, and even then ptomains which had previously 

 been formed in the food would not be rendered harmless. 



It is quite evident from these results that salt is an efficient food 

 preservative. It does not, however, destroy pathogens, and in 

 dilute solutions the organisms involved in food-poisoning may 

 develop. 



Chemical Preservatives. All authorities are agreed that the 

 preservation of food by drying, refrigeration, heating, canning, 

 salting, and preserving with sugar is justified on theoretical grounds 

 as well as practical experience, whereas the use of sulphites in sausage 

 and chopped meat, the addition of formaldehyd to milk, or of boric 

 acid or sodium flourid to butter are objectionable from the stand- 

 point of public health . The addition of sulphites to meat is especially 

 objectionable, as it places in the hands of the unscrupulous dealer a 

 method of concealing the signs of decomposition in meat, in addition 

 to being injurious to the health. 



The use of other preservatives such as benzoic acid and sodium 



