Page:Principles preservation fish by salt.djvu/11

Rh cell. It dissolves in some of the moisture, forming a saturated solution. This solution is separated from the contents of the cell by a cell membrane which is more or less semipermeable. Water passes out of the cell to the salt and the processes of decay are stopped because of insufficiency of water. The membrane, not being absolutely semipermeable, permits some salt to enter and the fish remains salty. The contents left in the cell are proteins or the valuable food elements of the fish which, being colloids, are not permitted by the cell membrane to pass out. Thus water is extracted, salt enters, and the fish is preserved.

When the time comes to eat the fish the process is exactly reversed. The fish is bathed in pure water. The cell contents are more concentrated than the exterior, so water passes in. The cell membrane is to some extent semipermeable, so the protein does not escape, but the salt does. This exchange is carried to a point where the meat is again plump and a sufficient quantity of salt has been removed.

Thus by exposing the meat of fish to salt we have removed the water and caused some salt to enter the meat and have stored the fish. We have then by exposing the fish to water put water back in the cells and taken out the excess salt. The actual food material of the fish–the cell protein–is still where it was, for practical purposes unchanged. If every step has been scientifically correct we have at the end very nearly the fresh fish we had to start with. But there is the rub. At every turn it is possible to depart from the scientifically correct. The principles of osmosis here very briefly stated are the fundamentals of the art of salting fish. In all that follows there will be frequent occasion to refer to osmosis.

The preservation of fish by salt is practiced extensively in the cooler parts of the United States, but very little has been done south of Chesapeake Bay. The reason fish have not been salted in the warmer parts of the country is that the process has not been satisfactory. Repeated efforts to salt alewives on the St. Johns River in Florida previous to 1920 uniformly resulted in failure. In 1918 research on this problem was undertaken under the immediate direction of the writer. The results of a part of this program were published.

The hypotheses which guided this work were somewhat as follows: During the course of “striking through” the fish two things are happening–(1) the flesh is breaking down by autolysis (a process to be explained later) and (2) the salt is penetrating the flesh. Salt arrests autolysis when it arrives, but considerable damage may be done before the salt has reached the innermost parts of the fish. Now, these two processes—salt penetration and autolysis–are running a race, so to say. If the salt penetrates to the innermost parts before autolysis has destroyed them, the salt wins the race and the fish is saved. If before the salt can get to the innermost parts they have been decomposed by autolysis to an intolerable degree, then autolysis wins and the fish spoils. High temperatures accelerate both processes, but while accurate measurements have not been made we know