DORSAL BLOODVESSEL OF THE EARTHWORM. 271 



delicate clinical thermometers, in the form of thermo-couples, 

 which could be inserted into the mouths of the worms and pushed 

 on down into the stomach intestine. These thermo-couples 

 were made of No. 32 copper and No. 32 constantan wires. Any 

 difference in the temperature of the two junctions of the couple 

 sets up an electromotive-force proportional in its strength to 

 the amount of the temperature difference, and which can be 

 accurately measured by means of a delicate galvanometer. In 

 this particular work it was found that i C. was represented by 

 a shift in the reading of the galvanometer scale of about 16 mm. 

 As it was practicable to read to half millimeters it will be seen 

 that a temperature difference of 0.03 could be determined. 

 For a somewhat more detailed account of the method of tem- 

 perature measurements the reader is referred to another paper. 1 



The worm having been subjected to a given temperature for a 

 sufficient length of time to have become completely adjusted to 

 the new condition, the temperature of the worm was noted, and 

 the length of time required for a definite number of beats of the 

 dorsal blood-vessel, usually 25, was taken by means of a stop- 

 watch reading to fifths of a second. The worm was then changed 

 to another bath at a different temperature, allowed to remain 

 long enough to become thoroughly adjusted to the new condition, 

 and another reading of the rate of contraction of the dorsal blood 

 vessel made. From the data thus obtained the temperature 

 coefficient of the rate of contraction was calculated by means of 

 the formula referred to above. 



It may be said that all possible precautions were taken to 

 avoid serious errors in the work. Temperatures were determined 

 by making the readings of the galvanometer against a certified 

 thermometer calibrated to tenths of a degree C. The tempera- 

 tures of the various baths were kept as uniformly constant as 

 possible and the exact temperature taken each time a count was 

 made. Occasionally one is in doubt as to whether a 'contraction 

 of the dorsal blood vessel has actually taken place. In such a 

 case the reading was thrown out and another made so as to 

 make sure of the fact. The temperature of the room was kept 

 as constant as possible in order to avoid any changes of resistance 



1 Rogers, Charles G., and Lewis, Elsie M., /. c. 



