198 EXPERIMENTAL PHYSIOLOGY 



direct action of the drug upon the heart. This follows from the 

 experiment already demonstrated, in which the force of the heart 

 beats was directly studied (fig. 113, p. 143). 



The changes of rate of flow studied in association with the changes 

 in volume are of interest when connected with the observations which 

 show that rate of secretion of urine depends rather upon rate of flow 

 of blood through the kidney than upon changes in blood pi'essure — 

 though these must of course act secondarily. Increase in urine flow 

 being associated with a dilatation of the kidney vessels directly con- 

 firms this view. 



Action of Digitalin. — The effect on the blood pressure is a fall of 

 short duration followed by a rise of much longer duration. During the 

 rise the rate of heart beat is slower, but each beat is more forcible. The 

 changes in the kidney tracing are not synchronous with those of the 

 blood pressure. There is produced a slow constriction of the vessels 

 which reaches a considerable amount and is very persistent. Gradually 

 relaxation occurs and results in a greater volume than before the injec- 

 tion ; but finally there is a return after several minutes to the initial 

 volume. We must note that during the kidney constriction the passive 

 variations in volume due to heart beats are very well marked. These 

 only become masked or obliterated if the constriction be very great ; 

 as, for instance, after a very large dose of the drug. The alterations in 

 rate of urine secretion are interesting. During the period of constric- 

 tion the rate slows considerably, but is accelerated to a certain degree 

 during the subsequent relaxation. Neither the relaxation nor the rate 

 of flow ever attains to the same degree as that observed after an 

 injection of caffeine. 



Action of Neurine. — The tracing (fig. 159) is introduced here 

 because it forms a very good demonstration experiment. In the experi- 

 ment reproduced 05 c.c. of a solution, made by adding one drop of a 25 

 per cent, solution of neurine to 6 c.c. of 1 per cent. NaCl, was injected 

 into the external jugular of a dog. The effect upon the respiration is 

 very striking. After a brief period of delay the animal passes for a 

 short time into a series of short respiratory spasms, next the respira- 

 tion rapidly slows and ceases, to ultimately recommence, first with 

 some irregularity, then expiration becomes rapid and short and in- 

 spiration prolonged, the rhythm remaining regular. Changes in blood 

 pressure closely follow these changes in respiratory rhythm (see fig. 

 159). At first there is a slight fall, partly due to diminished force and 

 rate of the heart beat. This is followed by a marked rise in pressure 

 as the inspiratory gasps occur, and is accompanied by an acceleration 

 of the heart beat. Then follows a period of fall of pressure in which 

 the heart beat is slow r ed, and finally as respiration is once more 



