CHEMOTAXIS 57 



to the action of chemical agents. The capacity for endurance 

 may be increased by successive exposures to a series of solutions, 

 beginning with one of low concentration, and passing in succes- 

 sive periods to higher, or more concentrated ones. Thus Lopriori 

 found that while the streaming movements of protoplasm were in- 

 hibited by exposure to an atmosphere of one part oxygen and 

 four parts carbon dioxide, yet if the plant were first exposed to a 

 mixture of 25 parts of oxygen and 75 of carbon dioxide for a 

 time, it might then be brought successively into atmospheres con- 

 taining 80, 85, 90, 95 and even 100 parts of the gas without im- 

 mediate injury. The acclimatization of a plant to any trophic agent 

 of course carries with it a readjustment of the three critical points, 

 the optimum, maximum and minimum. The acclimatization of 

 the organism to a new intensity of one agent generally affects the 

 critical points in relation to others. 



91. The Changes which Ensue in Protoplasm During Acclima- 

 tization. It is possible that protoplasm ceases to manufacture any 

 one of the substances illy affected by the chemical agent, replac- 

 ing it by others not so readily disintegrated or formed into new 

 compounds. The endurance of Marsilia has already been pointed 

 out as an instance of the efficiency of a protective covering as a 

 shield against chemical reagents. It is possible that this method 

 may be employed in some cases of acclimatization. 



92. Chemotaxis. Many organisms have acquired the power 

 of adaptive movement in response to the presence of chemical 

 substances serving as food, or as accessory reproductive devices. 

 Such movements are exhibited by roots in their movements 

 through the soil, by the absorbing organs of the lower forms, by 

 the pollen tubes of the higher plants, and by nearly all free motile 

 organisms. The connection between the molecular structure of 

 the stimulating substances and the amplitude of a response, has 

 received but little investigation ; it seems quite probably however, 

 that the chemotactic influence of many compounds may be at- 

 tributed to the action of the dissociated ions, although in this as 

 well as in toxic action the undissociated molecules of the same 



