CHAPTER XXII 



THE LATENT PERIOD AND REFRACTORY PERIOD 



The determination of the latent period in Mimosa — Experimental arrangements 

 for obtaining automatic record -Prolongation of latent period by cold — Spark- 

 record for determination of latent period — Prolongation of latent period by 

 fatigue - Sluggishness of the response of Philanthtis urinaria, also long latent 

 period and very protracted period of recovery — Latent period reduced under 

 strong stimulation — Response in Biophytum on the ' all or none ' principle — 

 Definite value of effective stimulus— Phenomenon of refractory period in 

 Biophytum — Parallelism of responses in Biophytum and in cardiac muscle — 

 Additive effects— Inappropriateness of term ' refractory period '— Energy in 

 excess of effective stimulus held latent for subsequent manifestation. 



Having explained the means by which it is possible to 

 apply a quantitative stimulus of uniform or increasing 

 intensity, and also how the responsive effect and its time- 

 relations are accurately recorded, we shall next turn to the 

 study of the various characteristics of the response itself, as 

 given for example by the plant Mimosa or BiopJiyiinii. In 

 order that we may inspect different parts of the response- 

 curve in greater detail, it will be necessary to take the record 

 on a fast-moving drum, so that the curve may be drawn 

 out, and its several features more easily distinguished. As 

 we wish, moreover, to study the excitatory effect on the 

 motile organ, stimulus will be applied directly on the 

 pulvinus. 



Automatic method of record. — As it will be necessary 

 in the course of the following investigation to measure the 

 times of reaction accurately, to small fractions of a second, 

 the record must be obtained automatically. It is to be 

 remembered that, as said before, response in vegetable tissues 

 is relatively more sluggish than in animal, and it is super- 

 fluous to arrange for measurements of time up to more than 



