138 



Chapter IX 



that the blood pressure of a monkey will fall to a little over half its 

 former value if but 0*0005 gram of the drug is injected intravenously. 

 How incredibly small a quantity of "/3-I" would suffice to produce 

 dilatation in an organ of a few grams weight, such as the monkey's 

 pancreas, were the drug produced in the organ itself. 



Truly no great eifort of the imagination is necessary to conjure up 

 such a mechanism as I have outlined. Our first concern is to inquire 

 whether there actually exist cases of dilatation of which there is no 

 other satisfactory explanation than that of a local chemical action. 

 The chain of evidence appears to be most complete in the case of the 

 submaxillary gland. 



In the cat stimulation of the cervical sympathetic nerve is known 

 to give a greater secretion of saliva in relation to the size of the 

 submaxillary gland than in other animals. The cervical sympathetic 

 also contains constrictor fibres running to the blood vessels of the 



10 



FIG. 74. Monkey. A.C.E. Arm volume and blood pressure. Effect of 0-5 mgm. /3-I. 



gland. Stimulation of this nerve produces in succession the following- 

 effects upon the blood-flow from the gland : (1) decreased, (2) in- 

 creased, and (3) decreased blood-flow. The second period or period 

 of dilatation comes immediately after the secretion of the saliva. In 

 Fig. 75 is shown the rate of flow of blood through the submaxillary 

 gland in a typical experiment. If we seek the cause of this dilata- 

 tion, which may be obtained in an even more striking fashion by the 

 injection of adrenalin, we shall see to start with that it cannot be 

 ascribed to mere loss of tone of the arterial wall, such as might be 



