114 



Scientific Proceedings (38). 



1. When substances that have been shown by special experi- 

 ments to exert a selective peripheral action are injected into the 

 circulation of an intact animal, the results frequently point to some 

 additional central action that tends to mask or to neutralize to 

 some extent the usual peripheral action. 



2. Substances that have an essentially central action may some- 

 times produce results to be explained only on the basis of an added 

 peripheral influence. 



3. In experiments accompanied by a condition of extreme low 

 blood pressure it is often difficult to know whether to ascribe these 

 final results directly to the primary assault on the central or peri- 

 pheral mechanism respectively, or to the additional secondary 

 effects produced by the cerebral anemia that is the concomitant of 

 the lowered systemic blood pressure. It is evident, therefore, that 

 a knowledge of the extent and importance of the part played pri- 

 marily by the central and peripheral mechanisms respectively, and 

 by the central mechanism secondarily, in the production of any 

 given result, is necessary for the interpretation of the mode of 

 action of the substance used. 



The chief difficulty is the impossibility in an intact animal of 

 limiting a substance to the cerebro-medullary, as contrasted with 

 the spinal and peripheral portion of the vasomotor system, or vice 

 versa. It was apparent that this difficulty could be overcome only 

 by isolating the circulation of the head and neck from that of the 

 trunk and then transfusing the blood from another dog. If this 

 could be accomplished it would be possible to obtain relatively 

 pure central and peripheral results by the injection of solutions 

 into either of the two independent circulations. The following pro- 

 cedure has been worked out on the dog. 



Under full ether anesthesia, the right common carotid artery of 

 the animal to be experimented upon, called hereafter the recipient, 

 is freed for its entire length and a ligature is placed loosely about 

 it. When it is desired to have none of the injected solution reach 

 the donor's circulation, and in short experiments, the external jug- 

 ular vein on the left side is similarly freed and is later used for the 

 outlet of the venous blood. The femoral artery is prepared for 

 taking manometric records and likewise the saphenous vein of the 

 opposite side for the injection of solutions into the circulation of 

 the trunk. 



