Transmission-time of Reflexes in Spinal Cord of Frog 5 



applied, svas so easily detected and measured in the direct response of the 

 muscle, that allowance for it could be made in estimating the time which 

 elapsed in the cord. 



II. The Same-Limb Reflex Time in the Normal Cord. 



It is essential for measuring the transmission-time in the cord that the 

 .stimulus should be instantaneous and single. To overcome the well-known 

 difficulty in producing a reflex eflfect by a stimulus of this kind without 

 the aid of drugs, I have had recourse, in part, to a method recommended by 

 Biedermann,^ which consists in keeping the decerebrated frog at a low 

 temperature (2°-6° C.) for from one to Ave days before making the experi- 

 ment. (Animals caught in warm weather were kept in the cold for some 

 days or weeks before being decerebrated.) 



The species used was Rana temporaria. For the most part the 

 specimens were small, the body length being about 6 cm. They were 

 decerebrated by section through the optic thalami in the way recommended 

 by Goltz,'^ the great advantage of which is that it is easily accomplished, 

 with little shock, and little, if any, loss of blood or disturbance of circulation. 



After ligaturing the iliac artery on one side, the sciatic nerve was freed, 

 so that a pair of needle electrodes could be placed on it without coming in 

 contact with any other part of the preparation. The corresponding 

 gastrocnemius muscle was then prepared, and, the whole preparation being 

 then placed in a moist chamber, its tendon end and a spot on its dorsal 

 surface were connected by non-polarisable electrodes with the Hg and 

 H2SO4 respectively of a capillary electrometer, which was clamped on to 

 the stage of a horizontally-placed projecting microscope. The vertical slit 

 upon which the column of mercury was projected, and the cylindrical lens 

 about 10 cm. behind it, were fixed in the front wall of a long dark-box. 

 Inside this box a trolley for carrying the photographic plate was arranged 

 to run at equable rates, special care being taken that in so doing it should 

 produce no vibrations. The distance of the plate was such as, with the 

 objective used, to magnify the image about 300 times. As the trolley 

 passed the slit, it broke a platinum contact which had been completing a 

 circuit containing a single Daniell cell and the primary, core-less, coil of 

 a Kronecker inductorium. The induction current that it thus produced 

 in the secondary circuit was used for exciting the sciatic nerve, the flne 

 (steel) needles which served as exciting electrodes being placed, 2-3 mm. 

 apart, on the nerve. There was always, unless the contrary is expressly 

 stated, a large resistance in the secondary circuit.^ The length of the nerve, 

 the position of each needle with regard to it, the length of the nuiscle, and 

 the distances of the two tied-on, leading-ott" electrodes from its ends, were 

 all carefully measured and noted. While the plate was pas.sing behind 



» Biedermanii, A. f. d. ges. Pliysiol., l.\.\x., 1900, y. 408. 



-' Goltz, Beitnige zur Leliie der Nervenceutreii des Frosches, Berlin, 1809. 



■■' I used one of 60,000 oluns. 



