Page:Principles preservation fish by salt.djvu/25

Rh Every species of bacteria is acclimated to some particular set of conditions, some of them almost incredible for living things. These red bacteria are accustomed to live and grow either on moist salt or very strong salt solutions. If bacteria are particularly resistant to some condition, as to strong salt in this case, it does not follow that they are likewise resistant to all severe conditions. It is the bacteriologist's business, by studying all the habits and peculiarities of the organism, to discover its weakest point where attack will destroy it. The strongest resistance of these bacteria, that against salt, is also the weakest, for it has been found that water less than 15 per cent saturated destroys them. Thus, the present indications are that the best and simplest remedy for the trouble is clean, fresh water and plenty of it. There is some evidence that may support the view that the usual impurities in salt, calcium and magnesium compounds, are essential to the growth and multiplication of these bacteria. The implication here is, of course, that pure salt itself would be a poor supporter of the bacteria. Of course, it would be futile to try to stop the reddening of cod as long as every shipment of salt brings new infection, and the butts, floors, buildings, and the surroundings at packing plants are heavily infected. Facts already given indicate also that for other reasons salt free from impurity is better. The results of the study of reddened cod only emphasize this advice.

The research on reddening should not, however, end here. We are again dealing with questions of permeability. The bacteria are adjusted to strong salt solutions, that is, the body fluid is of such concentration and their covering membrane is of such partial permeability that when surrounded by strong salt solution they live normally, but when water or weak brine surrounds them these relations are disturbed and they die. Probably water enters the cell in excessive quantity. It is known that the reddening does not attack fat fish. Perhaps the fat acts directly on the membrane, or indirectly by acting on the calcium and magnesium in the salt, to effect the disturbance.

Even crude salt now costs considerably more than coal. Yet the fish packers, who are usually very careful to economize in coal, are prodigal in the use of salt. Every hundred pounds of brine that goes overboard contain about 26 pounds of salt, to say nothing of the valuable nitrogenous matter that the brine has extracted from the fish. Considerable work has been done by the writer and his associates on the development of a process to recover salt and other substances of value from old pickle by precipitating the proteinaceous matter with sodium silicate. A trial plant was in use and under observation at an important fish-packing establishment for over a year but was not satisfactory under the circumstances. Brine pure enough for use was recovered, while a substance very rich in nitrogen was yielded as a by-product. This substance in the dry condition is nearly white and friable and contains enough nitrogen to command a handsome price as fertilizer if suitable for that purpose, but it may be more valuable for other uses. The method recovered brine, and for this reason some other method that would