PROTOPLASMIC MOVEMENT. 397 



neous injection as to kill them, and have observed the lymph- 

 corpuscles after some hours in active movement. 



V. Behaviour of Protoplasm tov^ards Artificial 

 Stimulation. 

 Protoplasmic contractions may, like the movements of 

 muscles and other excitable organs, be called forth, not only 

 by the normal physiological stimulus, but by numerous ex- 

 ternal influences, so-called artificial stimuli, or, as is more 

 frequently the case, existing movements can be thus influenced. 

 These stimuli are in reality the same as those for other ex- 

 citable structures ; as a general rule, any disturbance of the 

 electrical equilibrium acts as a stimulus when it takes place 

 with a certain rapidity or exceeds a certain amount, also, 

 all electrical impulse, change of temperature, mechanical or 

 chemical influence. 



The amount of irritability, as measured by the weakest 

 stimulus which calls forth an effect, varies with the kind of the 

 protoplasm, the kind of stimulus, and the special conditions. 



The protoplasm of fresh-water Amoebse, Diatoms, Valis- 

 neria, &c., behaves to very weak induction currents in the 

 same manner as do blood-corpuscles.^ 



The protoplasm of Pelomyxa, which otherwise is not spe- 

 cially sensitive, is violently affected by suddenly admitted 

 strong light, which has not necessarily any stimulating eff'ect 

 upon other kinds of protoplasm.^ 



The general conditions which aff'ect artificial stimulation, 

 with which it increases or diminishes, are the same as those 

 which aff'ect the power of spontaneous movement. They have, 

 however, rather wider limits, as is shown, amongst other 

 things, by the fact that artificial stimuli are potent even after 

 spontaneous movements have ceased to exist (e.g. as a result 

 of cooling, warming, withdrawal of oxygen, excess of COg).^ 



1 Author's observations. 



^ Th. W. Engelmann, " Ueber Heizung contractilen Protoplasnias durch 

 plotzliche Beleuchtung," 'Arch f. d. ges. Physiol.,' xix, p. 1, 1878. 



3 Cf. Kiihne, ' Unters. iiber das Protoplasma, fee.,' pp. 45, 53 (Amoebje), 

 p. 106 (Tradescantia). 



