396 GENERAL PHYSIOLOGY 



that in this depressed condition the vital processes are not wholly 

 extinguished, that a vita minima exists. Decisive experiments 

 upon this point are wanting. 1 



These phenomena of depression by cold are, however, not the 

 only ones that are called out by changes of temperature. High 

 degrees of heat, like low degrees of cold, depress vital phenomena. 

 It has been seen that increase of temperature acts to stimulate, and 

 that at a certain height the vital processes can become even violent. 

 But, if the temperature rises beyond this point, the intensity of the 

 processes suddenly decreases with extraordinary rapidity, and 

 vital phenomena become imperceptible. With yeast-cells warmed 

 above 40 C. no evolution of carbonic acid can be observed in a 

 solution of grape-sugar ; the eggs of sea-urchins undergoing 

 division or fertilisation, when warmed above 30 C., are at a stand- 

 still in the stage in which they already were ; amoebae warmed 

 above 35 C. maintain their spherical shape ; and at the same 

 temperature the cilia of ciliated cells remain greatly curved, i.e., 

 in the state of contraction ; in brief, the protoplasm falls into heat- 

 rigour (Fig. 183, B). If the objects are cooled after a brief action 

 of these high temperatures, they recover slowly ; but, if the action 

 continues too long, or the temperature rises a little more, a return 

 to life is impossible. The point where the vital processes act 

 most intensely, i.e., the maximum of metabolism, is, therefore, very 

 near the point of heat-rigour and the maximum of temperature, 

 beyond which death results, while it is very far removed from the 

 point of cold-rigour and the minimum of temperature. In 

 other respects the analogy between cold-rigour and heat- 

 rigour is complete ; both are phenomena of depression. 

 It is, therefore, disadvantageous, and it leads to false ideas, 

 to employ the expressions cold-tetanus, and heat-tetanus for 

 cold -rigour and heat-rigour, as is sometimes done. Rigour is the 

 direct opposite of tetanus : rigour is a phenomenon of depression, 

 tetanus a phenomenon of excitation. Cold- or heat-tetanus 

 cannot be produced at all, since the rhythmic intermittence of the 

 stimulus belongs to the conception of tetanus, and in temperature 

 this can hardly be obtained. Hence, confusing the two conceptions 

 leads only to erroneous ideas. 



Thus, life is embraced between two points of temperature, that of 

 cold-rigour and that of heat-rigour, at which the vital processes have 

 their minimum, or are at a complete standstill. Between these 

 points they go on perceptibly, and the more actively the more the 

 temperature rises from the point of cold-rigour up to near the 

 point of heat-rigour. Shortly before the latter point is reached the 

 vital processes have their maximum. From here on their intensity 

 suddenly sinks with increase of temperature up to the point of heat- 

 rigour. Hence, if we had an exact measure for the intensity of every 



1 Cf. p. 376. 



