STIMULI AND THEIR ACTIONS 471 



a larger number of phenomena before generalising. Nevertheless, 

 large number of discoveries speak directly in favour of the idea 

 here expressed. 



E.g., with increasing cold the energy of vital phenomena sinks, 

 until at certain low degrees of temperature, which likewise are 

 very different for different objects, apparently complete paralysis 

 results. The experiments of Klihne ('64) on Ammla, in which 

 the protoplasmic motion was at a complete standstill in cold- 

 rigor at 0° C, as well as a number of other phenomena previously 

 spoken of, afford examples of this. Further, with decrease of 

 moisture the intensity of vital phenomena sinks, until the latter 

 come to a complete standstill. The behaviour of dried, apparently 

 dead, organisms illustrates this. Finally, with decrease of food 

 and of oxygen vital phenomena are depressed, and, as is instanced 

 by the protoplasmic movement of Amaba in Kiihne's experiments, 

 cease in an atmosphere of pure hydrogen. 



The fact cannot be overlooked that there are cases in which 

 with falling temperature, as in the regulation of heat by warm- 

 blooded animals, or with decrease of the water-contents, as in 

 drying nerve and muscle, or with decrease of oxygen, as in the 

 asphyxiation of warm-blooded anirnals in a space free from oxygen, 

 phenomena of excitation are apparent. But the mode of occurrence 

 of these phenomena, which can be investigated in the cell-com- 

 munity only with difficulty on account of the complexity of the 

 conditions, is in large part still obscure, and many investigations 

 directed toward this point alone, especially in single cells or simple 

 tissues, are needed, before it shall be known clearly whether the 

 principle observed in so many cases, that with decrease of the 

 various vital conditions a gradual depression of vital phenomena 

 comes in without previous excitation, reallj^ has general applica- 

 tion. The question whether within the two extreme limits of 

 vital conditions living substance possesses but one maximum of 

 excitation is surely interesting. There are doubtless many cases 

 in which both augmentation and diminution of the vital condi- 

 tions produce depression, and in which between these two points 

 excitation rises to a single maximum. 



3. Death hy Ovej^-stimulation 



The inevitable end-result of continual or strong over-stimula- 

 tion is death, but the manner in which it develops differs in 

 individual cases according to circumstances. 



With continued, not too strong stimulation death develops fairly 

 gradually, and here the stages of the reaction can be followed best. 

 The effect of narcotics may serve as an example. If, e.g., an 

 infusorian cell, such as the ciliate Spirostomum, be exposed to the 

 influence of the vapour of chloroform or ether, there is seen first a 



