122 Blood Flow and Secretion 



components of the secretory apparatus under various conditions. 

 Unfortunately, little is known about this, much less than in the kid- 

 ney. Arteriovenous anastomoses have been found in the salivary 

 glands (Holzlohner and Niessing, 1936; Spanner, 1937, 1942). It has 

 been assumed that the striking increase in blood flow during chorda 

 stimulation is mainly due to the opening up of these anastomoses, 

 and that in the capillaries of the activated secretory alveoli the 

 blood may even stagnate (Holzlohner and Niessing, 1936). The 

 latter statement has, however, been disputed (v. Brucke and 

 Zwiauer, 1938). It may be that when the stimulation of the chorda 

 starts, the flow of blood in these vessels momentarily slows down 

 or even stops because fluid is lost to the saliva, and possibly also 

 because the capacity of the vascular bed is suddenly increased 

 through the activity of vasodilator nerves. Further work on the 

 role of the arteriovenous anastomoses of the salivary glands is 

 desirable. Some knowledge of the distribution of the blood within 

 the parotid gland of the dog has recently been gained by Burgen 

 and Seeman (1957). From studies on the iodide clearance of that 

 gland these investigators concluded that the rate of blood flow 

 through the capillaries enveloping the ducts is very high and that 

 the blood perfusing the ducts also perfuses the acini through a 

 portal system. For the present, however, it seems necessary to 

 resort to estimations of the total flow of blood through the gland 

 when investigating the effect of variations of the blood supply on 

 the secretion. 



In the following the various types of vasomotor fibres assumed 

 to innervate the salivary glands will be discussed separately; in the 

 different sections examples of the interaction between secretion 

 and blood flow will be given. 



SYMPATHETIC VASOCONSTRICTORS 



The presence of sympathetic vasoconstrictor fibres for the sali- 

 vary glands has been recognized since the time of Claude Bernard. 

 In his classical experiments on the blood flow through the sub- 

 maxillary gland of the dog (1858) he demonstrated that the venous 

 blood emerging from the gland turned brighter and flowed quicker 

 when the sympathetic trunk was cut in the neck; a permanent vaso- 

 constrictor tone in the gland was thus discovered. When the peri- 

 pheral stump of the nerve was stimulated the blood became dark 

 and the flow decreased or ceased completely. 



