GENERAL SURVEY 357 



under greater depletion, a strong stimulus evokes only a 

 single response (p. 316). 



Desmodium leaflets in a state of standstill give a single 

 response to a single induction shock of moderate intensity. 

 In a typical case the latent period was found to be '4 second, 

 the apex time 45 seconds, and the period of relaxation 

 120 seconds. The response curve exhibits a flattened top. 



In summer a single pulsation of a vigorous leaflet of 

 Desmodium is accomplished in the course of about 100 

 seconds. The quicker down movement is completed in 

 41 seconds, the maximum rate being -g mm. and average 

 rate -44 mm. per second. The period of up movement is 

 slower, being 60 seconds ; maximum rate of up movement 

 is -56 mm. per second, the average rate being 3 mm. per 

 second. 



The pulsating activity of the detached leaflet of Des- 

 modium can be maintained uniform for several hours by 

 subjecting it to a moderate internal hydrostatic pressure. 

 When the internal hydrostatic pressure is increased, the 

 limit of diastolic or up movement is increased ; the con- 

 tractile movement being opposed, the systolic limit is 

 decreased. Under increasing external load the pulsation 

 is decreased in amplitude and is finally arrested (p. 301). 



Similar Characteristics of Rhythmic Pulsation 

 in Animal and Plant 



The rhythmic tissues of the plant exhibit characteristics 

 which are extraordinarily similar to those of the rhythmic 

 tissue of the animal. The cardiac tissue of the animal has 

 a long refractory period ; the tissue takes no account of 

 a stimulus which falls within the refractory period. This 

 is also characteristic of the response of the rhythmic tissue 

 of Desmodium (p. 310). The rhythmic tissues, animal and 

 vegetal alike, are incapable of tetanus. 



By the application of Stannius' ligature the pulsation 

 of the heart is arrested at diastole. A similar arrest at 



