232 TRANSMISSION OF NERVE NET OF CGELENTERATES 



animal contains a nerve net and hence may serve as a region in which 

 to measure the rate of transmission in that type of nervous tissue. 



The method employed in this procedure was that long since used 

 in the measurement of nerve rates. A stimulus was applied to the 

 distal end of the tongue (Fig. 1,2), and the time intervening between 

 the moment of application and the moment of response was measured. 

 The stimulus was next applied at the root of the tongue (Fig. 1, 3), 

 and the time between the moment of application and the moment of 

 response was again measured. The difference between the amounts of 

 time consumed in these two operations represents the time necessary 

 for the transmission of an impulse from the distal end of the tongue 



Fig. 1. Oral view of a Metridium showing the tongue of tissue cut from the 

 pedal margin of the column, the three points of stimulation, 1, 2, and 3, and the 

 region of the lip into which the hook was inserted. 



to its root, a distance that is easily measured and that thus affords 

 a basis for the determination of a rate. 



The records of the several operations necessary in these measure- 

 ments were made in the usual way on a kymograph. Time was re- 

 corded by a marker actuated by an electrically driven tuning fork 

 at the rate of 50 vibrations per second. The moment of applying 

 the stimulus was recorded by a second marker which was activated 

 electrically from the same switch through which the stimulating cur- 

 rent was sent. This consisted of a faradic current that was disa- 

 greeably strong to the human fmger. It was applied by appropri- 

 ate electrodes to the portion of the pedal edge of the sea anemone 

 that was to be stimulated. This edge, as is well known, is extremely 



