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times, the practical industry has attached especial importance to the varying quantity 
of fat, primarily on account of the nutritive value which it represents, the importance 
of the fish as an article of human consumption depending to a great extent upon the 
amount of fat contained. Moreover, the fatty matter is contained in special organs, or 
at any rate, in such a manner as to render it possible to form, by immediate observa- 
tion, and without any complicated scientific aids, an approximate quantitative estimate 
of the amount. Finally, the quantity of fat discernible appears to stand in some relation 
to the general condition in point of nourishment, and thus serves to express the quality 
of the fish as a whole. 
The quantity of fat may be determined by two methods, of which the one supple- 
ments the other, both being therefore desirable. One is the process of chemical ana- 
lysis, the other examination (sometimes measurement or weighing) of the organs, 
where the fat is chiefly deposited, (the “ister” of the herring, and the liver of the 
cod). 
Variation in quality of the herring; varying amount of “ister’’. 
As mentioned in Chapters I and II, a great amount of material has been obtained 
during the last few years, by the collection of numerous samples, from which to study 
the natural history of the herring. For each separate collection of scale samples we 
have statements as to the length, weight, and degree of maturity of the mdividual, and 
also as to the quantity or size of the “ister”. The “ister’’ is the fat-containing organ which 
surrounds the intestines of the herring, and plays a most important part in the process 
of nutritive assimilation. We may here, as in the case of the genital organs, distinguish 
between different stages of developement, I, II and III, I here indicating small, IT medium 
and III large ister. These distinctions are naturally not absolutely exact, but with prac- 
tice, a high degree of accuracy may be attained in classification. It is then also possible 
to sort a large sample by determining what percentage of fish fall to each degree, and 
also to calculate the average quantity of ister for the whole sample. 
An examination, on these lines, of 100 first year fish from Nordland in 1912 gave 
the following results: 
8 fish with large ister, class III 
51 » » medium » » ul 
41 » » small » » I 
The average is thus 1.67, i.e. the majority of the fish fall between the I and II classes, 
(small and medium ister). 
We may next consider a large sample of fat herring, consisting of 610 fish taken 
in Nordland in August 1909 and examined as to age, length, and quantity of 
ister. The results of these investigations are shown in the following table, the percentage 
of each of the three fat classes being stated for each year group represented in the sample. 
Tt will be seen that these fat herring, of from 23—27 cm. length and 2—6 years of 
age, exhibit a far greater quantity of ister than the young fish referred to above, the 
average being very near Class III. The youngest of the fat herring, fish of 2 and 3 years 
old, stand highest, with a percentage of 2.92 and 2.96 respectively. 
All these fat herring are immature; in the case of the mature fish, the large herring 
22 
