CHEMICAL composition of food-fishes. 
699 
mine the percentage of water, and extracted with ether until free from 
fat, usually 2 or 3 hours. The crude extract, minus the water, fat, and 
ash, is reckoned as pure extract, and is designated as u extractive mat- 
ters.” It of course contains the albumen which was not coagulated, the 
other nitrogenous compounds, the carbohydrates, and whatever else, 
except fats and mineral matters, was taken from the flesh of the fish by 
the digestion in cold distilled water. 
Hot-water extract. u Gelatin .” — The residue left after the extraction 
with cold water was treated for 18 to 24 hours, generally about 20 hours, 
with distilled water at 100° or slightly below. It was then filtered 
through weighed asbestos filters, and the filtrate evaporated to dryness 
in platinum, and weighed as u crude gelatin.” In this fat and ash were 
determined, and the pure extract, called in the tables “ gelatin,” esti- 
mated as in the cold-water extract. It should be stated that in both 
hot and cold water extracts the figures for total exitract in the tables 
represent water-free substance, i. e., crude extract minus water. I am * 
inclined to think it would be better to determine both water and fat in 
the crude extracts in one operation by extracting with ether and noting 
the loss. 
Insoluble protein . — The residue left after the extraction with hot water 
was treated with alcohol or ether, or both, dried, and weighed. Water, 
ash, and fat were then determined (except, of course, that fat was not 
determined in the cases where it had been previously extracted). The 
ash was determined by direct burning, it being assumed that the pre- 
vious treatment with cold and hot water had sufficed to remove the 
easily fusible and volatile salts. The removal of the last portions of fat 
is often extremely difficult, and it is not impossible that in some cases 
traces were left and weighed as insoluble protein. The figures for total 
insoluble protein in the tables denote water-free substance. 
It is perhaps superfluous to state that the determinations were all 
made in duplicate. The figures given in the tables which follow rep- 
resent the averages of the closely agreeing results. The analytical 
details are given in the next chapter. 
3. DESCRIPTIONS AND DETAILS OP ANALYSES OF SPECIMENS 
OF AMERICAN FISHES. 
The usefulness of full statements of details of investigations of this 
sort is often insisted upon by chemists, and with justice. The attempt 
to properly collate and use results of other analyses of fish has im- 
pressed upon me anew and more strongly than ever the loss which such 
work often sutlers from omission of details in reporting it. 
The following data, regarding the analyses of fish and those of 
analyses of invertebrates, etc., beyond, have been compiled from our 
laboratory notebooks, the purpose being to make of them a faithful 
record of the facts regarding the specimens analyzed and the analytical 
results, and likewise to furnish such other data as, taken in connection 
