214 



Theories of Secretion 



B 



u 



Fig. io.ii. Schema of the close arterial injection type of experiment. 



Two substances A and B are injected into the blood supply of a salivary gland secreting at a 

 constant rate. Since substance A can penetrate the ducts at a more distal site than can substance B, 

 it appears in the saliva earlier than substance B as shown in the lower part of the figure. 



sensitivity is reached when a pair of isotopes are injected together 

 so that direct comparison of the outflow patterns is made on the 

 same samples of saliva. 



These methods have so far been applied only to the dog parotid 



6000 

 5000 



4000 



3000 



2000 



1000 



10 20 30 40 



* Sec 



50 60 70 80 



Fig. io. 12. The parotid gland of this dog was secreting at a rate of 4 /ul./g/sec. 

 At zero time tracer amounts of Na 22 and Br 82 were injected into the ipsilateral 

 carotid artery. Single drops of saliva were collected and analysed for the two 

 isotopes. 



Ordinate: counts per minute per drop of saliva. Note that Br appears in the saliva about 2 sec 

 (i.e. 8 /d./g) ahead of the sodium (Burgen, Terroux and Martin, 1960). 



