FUNCTIONAL VARIATION 109 



individuals at different times. They are variable not only in 

 degree but also in kind, and normal functions may be disturbed, 

 even altered, by external influences. Conversely, usual func- 

 tions may be discharged under most unusual conditions. 



All variation is either continuous or discontinuous, and contin- 

 uity must not be assumed. Many of the fundamental qualities 

 of living matter, such as definite composition, argue for discon- 

 tinuity. 



ADDITIONAL REFERENCES 



IMMUNITY AND ADAPTATION. Biological Bulletin, IX, 141-151. 

 GELDINGS MORE SUSCEPTIBLE TO DISEASE THAN MARES. Experiment 



Station Record, XI, 896. 



VARIATION IN IMMUNITY TO ANTHRAX (among sheep). By Martinet. 

 % Experiment Station Record, XIII, 186. 

 INSECTIVOROUS PLANTS. By Charles Darwin. 



For good evidence on functional variation consult the speed records 

 of trotting and running horses and the Advanced Registry of Jersey and 

 Holstein-Friesian Cattle. 



