Historical Introduction y 



stances to the tongue was abolished by section of the lingual nerve. 

 He discovered the very striking increase in gland blood flow that 

 accompanies secretion and noted the increased redness in the ven- 

 ous blood (1858). Another subject of contemporary interest was a 

 study on gland permeability to iodide, cyanide, dextrose, ferric 

 iron and ferricyanide. 



We have cited here only a tithe of the more important observa- 

 tions made by Bernard; his papers and, in particular, the 1856 lec- 

 tures referred to above, should be read by all students of salivary 

 secretion. They are a rich lode of information, much of it for- 

 gotten, and the experiments are models of how to conduct physio- 

 logical investigations and, above all, are presented with charm and 

 with style. 



In the latter half of the nineteenth century, salivary secretion 

 was a popular field of investigation especially in Germany and a 

 great deal of detailed and precise observation accumulated, the 

 extent of which can be seen in the masterly review by Heidenhain 

 in Hermann's Handbook of physiology (1883). Heidenhain himself 

 contributed greatly to this advance with studies on the cytological 

 changes in secretion, which have only been extended in recent 

 years by the use of the electron microscope. Heidenhain's school 

 also did much to develop physiological surgery. Pavlov carried this 

 technique to its extreme, studying the effects of the nervous system 

 on digestive canal secretion with great skill and insight. During the 

 course of these studies the conditioned reflex was discovered and 

 became the absorbing interest of Pavlov's life. One of Pavlov's 

 pupils, Babkin, became a lifelong student of salivary secretion and 

 through his two books and his students, has had great influence on 

 research on the salivary glands. 



In the modern period, the rationalization of the anatomy and 

 physiology of the autonomic nervous system brought about by 

 Langley's systematic study of the location of autonomic synapses 

 provided the basis on which Loewi and Dale developed the theory 

 of chemical synaptic transmission, which has had important con- 

 sequences in the understanding of salivary secretion. Langley's 

 account of the salivary glands in Schaefer's textbook (1898) remains 

 a model and a challenge to his successors. 



