PHAEMACOLOGY OF HYPOPHYSEAL EXTKACTS 757 



is due to some constituent of the posterior lobe, was the beginning of the 

 mass of studies that have been made of this portion of the hypophysis. 

 This investigator observed that when saline or glycerin extracts of the 

 posterior lobe were intravenously injected into dogs there occurred within 

 a few minutes a rise of blood-pressure which was quickly followed by a 

 fall. During this period the heart beat was somewhat slower and ap- 

 parently more feeble. The fall in blood-pressure lasted but a short time 

 and then rose again usually above the level obtained immediately succeed- 

 ing the injection. This second rise in pressure was accompanied by a 

 very marked slowing of the pulse rate that lasted for a long time and was 

 slowest at about the same time the pressure was at a maximum. When 

 the injections were made subcutaneously no distinct effect could be de- 



Fig. 6. Tracings which demonstrate the effect of the administration of 0.9 c.c. of 

 a 1:25 dilution of posterior lobe extract on the blood pressure and respiratory move- 

 ments. The upper curve shows the pressor effect and the middle curve records the move- 

 ments of the diaphragm. Time is in half minutes. (After Nice, Rock & Cortright, 

 Am. J. Physiol. ) 



tected on the heart or blood vessels from which observation it appeared 

 as if the active pressor substance of these extracts is destroyed or neutral- 

 ized in some way by the organism so that its effect is but temporary. 

 Howell also was inclined to believe that the heart and blood vessels be- 

 come less susceptible to subsequent injections since when these are given 

 the circulatory response is less marked or negligible. This immunity to 

 repeated injections cannot be attributed to a paralysis of the musculature 

 of the vascular system or their nerves, since no decrease of vascular tone 

 is observed. From the fact that the rise in pressure is more marked 

 after the vagi have been cut and also occurs after section and extirpation 

 of the cord below the medulla, Howell is of the opinion that the pressor 

 effect is probably mediated through the action of the substance in the 

 extract on the peripheral arteries and not through the central nervous sys- 

 tem. Schafer and Vincent (1899) confirmed HowelFs observation that 

 the pressor principle is confined to the extracts of the posterior lobe and 

 that immunity is exhibited to the effects of repeated injections. From 

 then on down to the present the studies of Magnus and Schafer (1901- 

 02) and others have demonstrated conclusively that the characteristic 



