TEMPERATURE AND AUTONOMOUS RESPONSES 339 



in plants in general, then the diminution of the amplitude of 

 its vibration with higher temperature is explained ; and I 

 shall be able to adduce independent proof that this is actually 

 the case in Dcsmodiuni, for we have seen that the external 

 indication of internal increase of turgor is the expansion of 

 the organ, which produces a movement upwards, the same as 

 that of relaxation. We found in the last series of responses 

 in fig. 141, moreover, that when the temperature was raised 

 gradually from the thermo-tonic minimum, the leaflet was 

 more and more erected, or ' relaxed.' Cooling, conversely, 

 produced diminution of turgor, and an opposite movement in 

 the direction of fall or contraction (figs. 140 and 141). 



The anomalous use of the word ' relaxation.' — We have 

 seen that the motile organ of Desmodium, when anaesthetised, 

 is brought to a state of standstill in a position of relaxation. 

 Its tonic condition, by virtue of which it exhibits contractile 

 response, has thus been abolished. We may then regard 

 ether as having brought about a loss of tone, or as having 

 reduced the tissue to the a-tonic condition. 



An apparently similar position of relaxation may, however, 

 be attained by the active process of expansion, which is the 

 result of an increase of internal turgor. It would thus appear 

 that we are liable to form many wrong inferences, as to the 

 tonic changes undergone by the organ, if we too hastily 

 conclude that expansion is always caused by loss of tone. 



Simple versus additive character of individual pulsa- 

 tions. — One question, regarding which opposite views have 

 been put forward hitherto, is that of the simple or composite 

 nature of the individual pulsations of cardiac muscle. The 

 movement of systole may, for example, be regarded as con- 

 sisting either of a single or of the additive effect of several 

 constituent contractions. In the production of tetanus in the 

 case of muscle and also in that of contractile vegetable tissue 

 we have seen several individual contractions, when following 

 each other with sufficient rapidity, become merged in one appa- 

 rently continuous contraction (figs. 49, 50). When less rapid, 

 however, they are individually distinguishable. Similarly, 



7. 2 



