in CHEMICAL VARIATION 117 



for instance, the percentage of the principal com- 

 ponents of the wool of some breeds of sheep 

 (after Miintz and Girard) : 



Dfchley. Merino, So log not. 



Water .................. 15 10 14 15-5 16 



Nitrogenous matters 63 48 53 64 53 



Fatty substances ... 8 30 19 6 10 



Ash ..................... ii 10-5 15 13 18 



Potash .................. 6 4-5 7 6-5 4-5 



While some components vary but slightly, such as 

 water and potash, others, such as fatty substances, 

 are found in very different proportions ; the difference 

 being from six to thirty, or from one to five. 



Similar variations are to be observed in the mus- 

 cular or fleshy parts. Sir R. Christison made 

 chemical analyses of salmon in good health and con- 

 dition, and of salmon after spawning. The results 

 are as follows : 1 



Healthy Salmon. Salmon out of Season. 

 Oil ............ 18*53 per cent. 1*25 per cent. 



Nitrogen ... 1970 17-07 , 



Salts ......... 0-88 0-88 



Water ...... 60-89 8o'8o 



It is not necessary to have studied physiology very 

 deeply to understand that such differences in the flesh 

 or skeleton, as are shown above, may be of great im- 



1 From a paper read in the Royal Society, quoted in the American 

 Naturalist, vol. vii., p. 372. 



