of the Fishery Board for Scotland. 



85 



Methods of Analysis. 



It was impossible to adopt many precautions which might have been 

 desirable, owing to the necessity for carrying through the analysis as 

 quickly as possible. 



Such estimations as these of the percentage of water in the muscles and 

 reproductive organs cannot be carried out in such a way as to absolutely 

 prevent loss of weight from any other cause than the removal of water. 



(1) Water percentages. — The skin was removed, then as much of the 

 the muscular tissue as could be conveniently obtained was minced up 

 extremely fine by being passed through a mincing machine. 



Specimens were taken between watch glasses and dried in a warm oven 

 at a temperature between 60°-70°C., under conditions where oxidation 

 was prevented as far as possible, the final drying being carried out in 

 vacuo. 



The same procedure was adopted in the case of the reproductive organs. 



(2) Nitrogen and Phosphorus estimations. — It was of course necessary 

 to estimate the amount of nitrogenous material in the muscles and 

 genitalia, and it was also thought advisable to estimate the amount of 

 phosphorus. 



The total nitrogen was estimated in a small portion of muscle and also 

 in a similar quantity of ovary or milt respectively, the method that was 

 adopted being that of Kjeldahl. 



For purposes of convenience the numbers for the total nitrogen are not 

 given in the tables, but are converted into terms of protein by multiplying 

 the amount of the total nitrogen by the usual factor, 6*25. This is, of 

 course, simply a matter of convenience, some of the nitrogen being present 

 in other forms than protein. As, however, by far the most important 

 nitrogenous constituent in the muscles and genitalia is the protein, 

 probably not more than 2 per cent, of other nitrogenous constituents 

 being present, it is sufficient to state the amounts of total nitrogen in 

 terms of protein. 



The phosphorus was estimated in a portion of the fluid obtained after 

 incineration by the Kjeldahl method. 



The fluid was rendered ammoniacal, then acidified with nitric acid, and 

 the phosphate then precipitated by ammonium molybdate. The phospho- 

 molybdate precipitate was subsequently dissolved in ammonia, and the 

 phosphate precipitated by magnesia mixture. The triple phosphate was 

 then received on an ash-poor filter paper, washed, dried, and incinerated. 

 It was then weighed and the weight of the Mg 2 P 2 0 7 was then calculated 

 in terms of P 2 0 5 , and given as such in the tables. 



(3) Fat. — The finely powdered dried material (muscles or genitalia) 

 was placed in a Soxhlet filter paper tube and extracted with ether in the 

 usual way for about 36-48 hours. Only about 3-4 grammes of the 

 dried material were taken, so that the extraction ought to have been fairly 

 complete. The fat was freed from ether and weighed in the usual way. 



In the tables the amounts of proteid, fat, and P 2 0 5 are given in two 

 forms, first, in grammes per 100 grammes fresh muscle and fresh ovaries 

 or milt ; secondly, in terms of grammes in total fresh muscle or genitalia 

 respectively, as calculated for the average fish of the batch under 

 examination. 



It was thought advisable not only to give the percentage amounts of 

 proteid, fat, and P 2 0 6 , but also the absolute amounts in the muscles and 

 genitalia respectively of the same fish. The weight of the muscles of the 

 fish was obtained roughly by deducting ^ of the total weight, this 

 fractiou being supposed to cover the weight of the head and bones. 



