472 



GENERAL PHYSIOLOGY 



stage of excitation, in which the ciliary motion becomes strongly 

 accelerated. Gradually with continued action the excitation gives 

 way, and there begins a stage of depression resulting in a complete 

 standstill of the cilia. From this stage by interruption of the 

 stimulus and the re-establishment of the normal vital conditions 

 the organism can be revived. If, however, the action continues 

 still further, this is no longer possible ; narcosis passes directly into 

 death. The same thing is seen in human ganglion-cells in 

 morphine poisoning. At the beginning of the action there is a 

 stage of excitation, which soon gives way to a complete paralysis 

 of the ganglion-cells. With too strong a dose the death of the 

 cells results ; this is seen in a standstill of the functions dependent 

 upon them (movement of the heart, respiration, etc.). The same 

 sequence of actions is produced by the thermal stimulus with 

 continual increase of its intensity. The protoplasmic motion of 

 Amoeba increases with increasing warmth up to nearly 35 C. 

 Here the motion suddenly diminishes ; the organism continues in 



FIG. 243. Pelomyxa palustrls. A, Creeping ; B, contracted as a result of feeble chemical Simula- 

 tion ; C, undergoing granular disintegration with long stimulation. 



the stage of contraction and performs at most very feeble motions. 

 With a slightly higher temperature the latter wholly cease. This 

 is the point of heat-rigor. Upon cooling from this point motion 

 returns. But, if the temperature rises above 40 C., the heat- 

 depression passes over into death. With thermal stimulation the 

 whole sequence of reactions from the minimum of temperature up 

 to the maximum is presented with the greatest clearness : stand- 

 still of vital phenomena in cold-rigor, increasing excitation, 

 depression in heat-rigor, and finally death. 



The complete series does not always appear. Very frequently 

 one or the other stage is wanting. This depends partly upon the 

 special qualities of the living substance, and partly upon the kind 

 of stimulation. Often under the influence of stimuli of very high 

 intensities all stages are omitted, and death results at once. 

 Sometimes there is a brief stage of excitation, but intense excita- 

 tion is followed immediately by death. If, while Pel.omyxa is 

 creeping quietly, it be stimulated only feebly by acids, alkalies. 



