THE SALTING OF FISH. 



47 



peratures. Such experiments would show whether these substances 

 are partially responsible for the spoilage. However, both the milt 

 and roe must be removed if all of the blood be taken out of the fish. 

 This is, therefore, a point of secondary importance. 



ACTION OF THE SKIN. 



The skin of fish is known to be a membrane which is more or less 

 impermeable to the passage of dissolved salts. In the work on pene- 

 tration of different salts it was noted that the penetration of salt into 

 the fish took place much more rapidly through the cut flesh than 

 through fish covered with skin. In the experiments on the penetra- 

 tion of salts containing calcium salts as impurity the passage of the 

 salt into the fish could be followed very easily, for as the salt passed 

 into the fish the fish became very white. This gave an easy way of 

 estimating the rate of penetration of the salt into the different parts 

 of the fish. The fish were cut on different days. The depth of the 

 whitening was measured and the cross sections were drawn to scale. 

 The diagrams are given to show how much more rapid the penetration 

 of the salt is through the cut surface than through the skin surface. 



Figure 6 shows the appearance of ji cross section of a squeteague 

 after it had been in salt for one da3\ The whitening had pene- 

 trated 5 nmi. on the cut surface, but the whitened condition was 

 found only 1 mm. under the skin. Figure 7 shows a cross section 

 of the fish after it had been salted for six days. At this time the 

 line between the light and dark portions of the section was not so 

 distinct. Figure 8 shows a section of the fish near the end of the 

 salting period, which was 10 days. There is yet a portion of the fish 

 which was not white. Tliis shows that the fish as yet was not 

 salted uniformly throughout. The fish became entirely white 

 throughout on the thirteenth day. 



In order to gain a more accurate idea of the retardation of the 

 penetration of the skin by the salt, some experiments were tried to 

 determine the relative rate of penetration of salt into skinned and 

 unskinned fish. In these experiments both skinned and unskinned 

 squeteagues ' were salted in dry salt by the ordinary procedure, as 

 described previously. The salt used contained 1 per cent of calcium 

 chloride. This is about the purity of the average salt used for the 

 salting of fish. 



The penetration of the chlorides into the fish was determined by 

 analyzing different sections of the fish from day to day. The pro- 

 cedure followed has been described in the first part of this paper. 

 The results of the analyses of the sections from one-half centimeter 

 to 1 cm. in depth are given in Table 13. 



Table 13. — Comparatrti: Rate of Penetration of Chlorides " Into Skinned 

 AND Unskinned Fish,* Expressed in Per Cent of Chlorine in Dry Fish. 



a Analysis of salt used, 99 per cent sodium chloride, 1 per cent calcium chloride. 

 6 Inner section of fish. J to 1 cm. 



