EXTERNAL INFLUENCES AS CAUSES OF VARIATION 265 



processes from the chemical standpoint that some substances 

 exert no influence upon protoplasm, while others kill it out- 

 right ; that some accelerate and others retard its normal action ; 

 and that some suspend activities more or less completely, while 

 others divert them into entirely new channels. Here is varia- 

 tion due to chemical disturbance of the material basis of life, 

 and it is well to study somewhat in detail this " modification of 

 vital actions " from chemical causes. 1 In studying this class of 

 phenomena it is necessary, of course, to make use of simple 

 organisms of one or of few cells, and while we cannot reason 

 directly from these to the higher animals and plants, still all 

 evidence goes to show that the differences- are not so much in 

 kind as in complexity. 



Oxygen. All experiments indicate that no protoplasm can 

 long survive in the absence of oxygen. In most cases it is taken 

 directly from the air, but in others, as in anaerobic bacteria, it 

 is probably extracted from surrounding compounds containing 

 oxygen. Diminished oxygen retards and increased oxygen and 

 ozone greatly accelerate the vital processes, 2 all without chang- 

 ing their character. 



A number of oxygen-containing substances greatly retard or 

 even destroy vital activities, probably through " oxidation of the 

 protoplasm." 3 If this be the case, and the material basis of 

 life is subject to the ordinary chemical process of oxidation, it 

 shows that vital processes in the last analysis rest upon a strong 

 chemical basis. 



Hydrogen peroxide (H 2 O 2 ), only slightly different from water 

 (H 2 O), is a powerful oxidizing agent. One part in ten thousand 

 (o.o i per cent) in hay infusion killed all ciliata in from fifteen to 

 thirty minutes. Algae survived a o. I per cent solution but ten 

 or twelve hours, and died in a 10 per cent solution in a few 

 minutes. " Salts of chromic, manganic, permanganic, and hypo- 

 chlorous acids act as intense poisons, apparently by directly yield- 

 ing oxygen atoms to the plasma proteins." Chlorin, iodin, and 



1 C. B. Davenport, Experimental Morphology, Part I, chap, i, from which the 

 data in this section are largely taken. 



2 Small animals confined in an atmosphere of pure oxygen exhibit greatly 

 increased activity and " live themselves to death " in a few hours. 



3 C. B. Davenport, Experimental Morphology, Part T, p. 3. 



