404 MICROBIOLOGY OF SPECIAL INDUSTRIES. 



and the whole mass of food substance is permeated by them. Potassium 

 nitrate (saltpeter) reacts with the flesh, being reduced in part to nitrite. 

 This enters into a combination with the coloring matter of meat, which 

 upon cooking produces the characteristic red color of saltpeter-cured 

 meat. 



The various manipulations during the process of pickling or dry 

 curing serve to introduce numerous microorganisms. Many of these 

 may flourish in the pickling fluids, but in a sufficient concentration of 

 salt and at a sufficiently low temperature, decomposition ordinarily does 

 not progress so as to become objectionable, and proteolytic decomposition 

 (putrefaction) is effectually prevented. This protection of the protein 

 depends to some extent upon the acidity of the medium, which in turn 

 is due largely to the bacterial decomposition of the muscle sugar. The 

 powerful putrefactive bacteria (B. cedematis group, B. putrificus) flourish 

 only in an alkaline medium. On the other hand too high a degree of 

 acidity becomes in itself objectionable on account of the sour or rancid 

 taste, and it is therefore important that the acid-producing bacteria should 

 be held in check somewhat. In practice, saltpeter has proved of value 

 for this particular purpose, and its action apparently depends upon the 

 antiseptic effect of minute quantities of nitric acid (HNO 3 ) and nitrous 

 acid (HNO 2 ) set free from the salt by the excess of organic acids produced 

 by the bacteria. The curing of meats by pickling solutions is often supple- 

 mented by desiccation and impregnation with the antiseptic substances 

 of wood smoke. 



The dry-salting of codfish is an example of preservation by increasing the osmotic 

 tension. The fish is cleaned and beheaded, split longitudinally, and the vertebral 

 column removed. It is then carefully washed, and all visible blood is removed. The 

 pieces are next covered with dry salt and packed in open casks. The salt rapidly 

 extracts water from the flesh and a strong brine results. After a few days the casks are 

 emptied out, and the pieces of fish, now smaller because of the loss of water, are again 

 thoroughly washed and again packed in dry salt so that the adjacent pieces of fish are 

 completely separated by an intervening layer of solid salt. The contents of the cask 

 is subjected to high pressure to remove air, and the cask is finally closed. 



The curing of hams is an example of preservation by increased osmotic tension 

 combined with the addition of chemical preservatives. After slaughter and chilling 

 the hams are injected with a solution containing 25 per cent common salt, 15 percent 

 granulated sugar, and 12 per cent saltpeter, and are then stored at a low temperature, 

 preferably between o and +4, in a brine containing about 20 per cent common salt, 5 

 per cent sugar, and i per cent saltpeter. The brine is renewed once or twice at intervals 

 of a week or ten days. After about a month the hams are washed in warm water, dried 



