SAirUEL ERNEST POND 811 



fiber impregnated with Bakelite; this substance is insoluble in the 

 solutions used, and does not affect the tissues. In the experiments 

 with the heart of Limulus the organ was fixed in a trough composed 

 of paraffin. 



The tissues were prepared as follows: Frogs were first curarized, 

 with about 2 cc. of a 1 per cent solution of curare (in Ringer's solution), 

 and after a period of 20 minutes both sartorii were removed. One 

 of the muscles was mounted on the support and the other kept in 

 cold Ringer's solution. The companion muscle was used in a few 

 cases in duplicate experiments. The ventricle of the turtle was re- 

 moved, cut into rings, and two of these opened up as strips of thick 

 muscular tissue. One was placed in position on the apparatus and 

 the other kept reserve for later use. The heart of the female Limulus 

 (in preference to the male because of its greater length) was removed 

 through a dorsal opening in the carapace and placed in the paraffin 

 trough with the ventral side up, so that the ganglion was completely- 

 immersed in the solution. On one occasion, the muscle tissue was 

 cut away from the ganglion between the third and sixth segments, 

 leaving the anterior and posterior segments connected by the ganglion. 



Complete records of one or more muscle contraction waves were 

 taken upon a strip of photographic film wrapped about a kymo- 

 graph drum. The procedure adopted was as follows: The tissue 

 was placed in position for a record, washed in at least two changes 

 of the test solution over a period of 15 or 20 minutes, and then 

 exposed to a final bath in which the records were taken. Limulus 

 hearts in the troughs were so arranged that the test solution flowed 

 slowly over and about the tissue; while the turtle and frog tissues 

 were exposed in tumblers holding about 250 cc. of solution. The 

 arc-lamp was lighted and adjusted to uniform illumination of the 

 mirrors; the tuning-fork was then started and the kymograph brought 

 up to speed. The latter was so arranged (inside of a light-proof 

 box) that a shutter on the arc-lamp remained open during one com- 

 plete revolution of the drum. An inductorium circuit was closed (in 

 response to a signal attached to the kymograph) shortly before the 

 shutter was opened and broken just afterward. Thus during one 

 revolution of the kymograph drum the tissue was stimulated and 

 one complete muscle record was made, together with the time curve. 



