ii6 A. P. Mathews 



so far as their action, stimulation or depression, on the motor nerve 

 was concerned. But it is clear from what has been said, that no 

 such simple arrangement is to be anticipated in studying a complex 

 system such as a cell undergoing rapid change. In such a system 

 all we observe from the action of the salt is a definite result, which 

 implies a certain change in the system. This result may be a stimula- 

 tion, such as a muscle contraction, or nerve impulse. Evidently 

 the same result may be brought about in several different ways: 

 either by direct action of the salt on the particular part of the system 

 which undergoes change ; or, indirectly, by the salt altering another 

 part of the system, so as to produce or check the result. It is con- 

 ceivable that the same salt may have a double action : by one action 

 tending to produce the direct change of the response ; and indirectly 

 by action on another part of the system having as a result the 

 setting-up a process which will check its own direct action. 



Something of this last process obtains, I believe, in protoplasm 

 generally, so that strict adherence to the law of ionic potential action 

 is not to be expected; but a general adherence is to be expected, 

 and the facts show it exists. 



An interesting example of this stimulating action is seen in 

 the extrusion of polar globules in Chaetopterus eggs. These eggs 

 undergo the first processes of maturation before they are shed, but 

 they do not extrude the polar globules until fertilized. The first 

 polar spindle is formed and comes to rest in the equatorial plate- 

 stage. Evidently in this egg there is not sufficient energy in the 

 spindle to overcome the resistance offered by the surface tension or 



TABLE lo. 



MiNiMUN Concentration of Various Salts Causing Extrusion of Polar 

 Globules in Chaetopterus. 



Salt Concentration 



Na3 citrate jjg n 



Na,S04 \ n 



KI <^^n 



KBr <^ n 



KCl ^s n 



NaCl /j « 



LiCl <i« 



CaClj tV '^ 



MgCl. o(?) 



MnCU o 



CdCU <i;5wr« 



^^^'2 < 24,500^ 



