362 MARINE PRODUCTS OF COMMERCE 



better in media containing 1 or 2 per cent salt than in similar media devoid of 

 this inorganic substance. Salt preserves fish by extracting water from them. If 

 fish are packed in a barrel of salt, the salt soon withdraws enough water from 

 the fish to form suflBcient brine to cover them. Simultaneously, with the extraction 

 of water salt passes into the tissues of the fish and the body juices soon become a 

 concentrated salt solution. When sufficient salt has passed in to coagulate the 

 proteins afi^ected by sodium chloride, and when the cells have shrunk because 

 of the loss of a large portion of their water, the inner flesh of the fish loses much 

 of its translucent appearance and stickiness and becomes, in the words of the 

 Salter, "struck through." The passage of salt from fish into water is an example of 

 osmosis; the skin and cell membranes act as imperfect semipermeable membranes 

 which permit outgo of the water and the entrance of some salt, but which prevent 

 loss of the colloidal proteins of the cells. The flow of water through semipermeable 

 membranes is always from the dilute to the concentrated solution. Thus, when fish 

 are placed in concentrated brine, water passes rapidly out of the cells of the fish 

 through the cell wall into the brine. If the fish are placed in dr\' salt, the moisture 

 on the outside of the fish dissolves some of the salt and forms a concentrated 

 solution which immediatelv causes the flow of water from the cells of the fish. 

 Salt from the brine slowlv finds its way through the cell walls into the protoplasm. 

 E\entually the concentration of the solution inside the cells of the fish tissues 

 equals that of the brine. WTien this condition has been reached, the salting process 

 is complete and the fish are said to be "thoroughly struck." 



Spoilage of fish is brought about chiefly by autolysis and by bacterial decomposi- 

 tion. In autolysis, chemical and physical changes are brought about by enzymes 

 contained in the cells of the fish after its death. It begins almost immediately after 

 death and proceeds most rapidly at a temperature of 98.4° F (36.9° C). The 

 lower the temperature, the slower the action. The blood, certain tissues, and 

 glands, such as the kidney, contain very active enz>Tnes. The autolytic enzymes 

 are most active imder slightly acid conditions; in alkaline media their activity is 

 greatly reduced. Dtuing rigor mortis the aciditv of the tissues decidely increases; 

 this change of the hydrogen ion concentration causes an acceleration of autolytic 

 decomposition. Enzymes are most active in dilute solution and do not act in the 

 absence of water. Most enzymes are destroyed or rendered inactive by concen- 

 trated salt solutions, therefore salting preserves fish from autolytic decomposition. 



Bacteria are unicellular organisms which, when placed in suitable media, mul- 

 tiply rapidly and produce enzymes which break down animal tissues and the 

 various organic substances contained in organic matter. Usually the body of the 

 fish contains few bacteria, aside from those in the alimentary tract. However, un- 

 less great care is used in handling the fish during cleaning and washing, many 

 bacteria are introduced into the fish. Bacteria grow rapidly at temperatures be- 

 tween ll-liy^ F (25-46.1° C). Between 30 and 50° F (- 1.1 and 10° C) most 

 bacteria grow slowly. While many grow readily in media containing as much salt 

 as sea water, if the amount of salt increases much above this point, the water passes 

 out of the cell and it collapses or reverts to the spore form. Thus, strong salt solu- 

 tions prevent bacterial growth. 



When fish are killed, autolytic and bacterial decompositions immediately begin. 

 At first only slight changes in the physical appearance of the fish are noted but, 

 if the fish are not chilled, they soon develop a strong odor and taste, the blood 



