1916 Smith; on Salmon Development 95 



from the dark weighed 11.28 per cent more than those from the light. 

 It is evident from the foregoing estimates, admitting some possible error 

 due to methods of removing water, that fish developed in the dark through 

 the yolk-sac stage have a very decided advantage over those kept in the 

 light. 



Chemical Analysis of Fish 



It was deemed important to determine just wherein the difference in 

 weight lies. To this end a careful analysis was made to find the relative 

 amounts of water, protein, fats, and ash in the fish of each trough. Fifty 

 fish were taken at random from each trough shortly before feeding began. 

 They were very carefully dried by the use of linen toweling and filter 

 paper after which they were exposed to the atmosphere until all visible 

 'moisture had disappeared from the surface. Those from the dark trough 

 then weighed 26.8422 grams, and those from the light 24.4216, the fish 

 from the dark being practically 10 per cent heavier than those from the 

 light. The fish were now placed in an electric incubator kept at a tem- 

 perature of 100°C., until all water was evaporated. The dried material 

 was then pulverized and carefully extracted with ether in a sochlet ap- 

 paratus until all oil was removed. The residue was then burned until 

 nothing but the white ash remained in the platinum crucible. Table 4 

 shows the weights in grams of the different substances in each group of 



Table 4. The relative weights of substances in each group of fish 



50 fish. It is evident that water makes the great difference in weight be- 

 tween the two groups of fish, but when we compare the per cents of sub- 

 stances in each group we find but a very small relative difference 

 (Table 5). 



Table 5. Per cents of substance in each group of fish 



Looking at the relations from this standpoint the difference in per 

 cents of w^ater between the two groups of fish is less than one-third of one 

 per cent while the differences in the other materials are still less. So, 

 from this viewpoint, the relative amounts of material in each group are al- 

 most identical. 



