Taylor. — Preservation of Fish by Salt 143 



be found that fat is also of the greatest importance, and re- 

 quires very careful consideration and study. All fishes have 

 some fat, but the quantity is variable from species to species, 

 between individuals of the same species, and within a single 

 individual from season to season. The distribution of fat 

 is also different in different species of fish. Some fishes, such 

 as herring, salmon and alewives, contain fat well distributed 

 throughout the body tissues. In others, such as cod and 

 haddock, the fat is localized in some particular part of the 

 body, as, in the species mentioned, the oil is contained in the 

 liver, the flesh being almost entirely destitute of oil. For 

 reasons that will be set forth later, fat fish must not be ex- 

 posed to the air because of untoward changes that air causes 

 in the fat; but no harm is done to the protein constituents. 

 Therefore fish which do not contain fat may be dried in air 

 after they are salted. 



In practice these differences are well recognized. In the 

 case of cod and haddock, in which the muscle tissue is free 

 from fat, the greater part of free water is extracted in the 

 usual way by salt, later assisted by the pressure of piles or 

 kenches in which the lower layers are pressed by the weight of 

 the upper layers in the kench, and finally by drying out-of- 

 doors or in artificial drying tunnels. Fish prepared by this 

 method are packed and shipped in the dry state, with advan- 

 tages in saving of freight and simpler handling in general. 

 In the case of mackerel and herring, and such other fishes as 

 have fat muscle tissue, the fish must at all times be carefully 

 excluded from contact with air. If the fish are directly ex- 

 posed to air for a time, the fish "rust," i. e., the fat becomes 

 reddened and rancid, and the value of the fish for food is very 

 greatly impaired. This rusting, especially of salt mackerel, 

 is of immediate and pressing practical importance, for there 

 is a regular waste of a large percentage of mackerel on our 

 northeastern coast for no other cause than rustiness and ran- 

 cidity. This aspect of the subject has not been investigated 

 to any great extent, but there is just as much reason to expect 



