Studies in Experimental Plethora. 191 



circulation. In view of the investigations of Dale and Richards 8 

 who found that the normal reactions of capillaries are not main- 

 tained when an organ is perfused with saline solution, whereas the 

 reactions of the arterioles are retained, it seemed not impossible 

 that Erlanger, Gasser and Gesell by their method tested largely 

 the reaction of the peripheral arterioles in shock, whereas the 

 optical curves analyzed by Wiggers determined peripheral resist- 

 ance changes due in part also to alterations in the caliber of the 

 capillaries, viscosity of blood, etc. Since evidence has accumu- 

 ated that the capillaries are particularly affected in shock it is 

 quite possible that their dilation might decrease the total resist- 

 ance early in shock in spite of the fact that a contraction of 

 their supplying arterioles occurs. If this be true the discordant 

 finds of Wiggers and Erlanger et al. would be explained. 



At the suggestion of Doctor Wiggers, we therefore attempted 

 to determine by direct methods how the total peripheral resistance 

 behaved during the course of experimental shock — particular 

 attention being directed to early phases. To do this we employed 

 the method described by Cope 4 which essentially determines the 

 rate that the animal's own blood flows through a limb temporarily 

 isolated from the rest of the arterial circulation. The results 

 obtained by this method at various times during the course of an 

 experiment were related not only to changes in mean blood pressure 

 and heart rate but to the contours of the optically recorded 

 carotid pulse as well. After preliminary ligation of the pelvic 

 vessels required for the procedure described by Cope, shock was 

 induced by the "gastric massage" method described by Hender- 

 son and Haggard. 5 



Results. — Thirteen experiments were carried out on anesthe- 

 tized dogs. Comparison of the optical curves before and after 

 ligation of the pelvic vessels revealed no changes such as were 

 found by Wiggers in the initial stages of shock. Arterial blood 

 pressure sometimes declined temporarily but recovery to or above 

 normal was usually prompt. Control tests of the total peripheral 

 resistance indicated that it usually increased for a time. 



3 Dale and Richards, Jour. Physiol., 1918, lii, 144. 



4 Cope, Amer. J. Physiol., 1911, xxix, 137. 



6 Henderson and Haggard, /. Biol. Chem., 1918, xxxiii, 136. 



