Historical Introduction 5 



lation as food in the mouth, and suggested that a nervous pathway 

 was involved; Midler's influence is apparent in this attitude. It was 

 reading Mitscherlich's paper that led Ludwig (185 1) to test experi- 

 mentally whether there was a secretomotor innervation of the 

 salivary glands. Ludwig investigated the anatomy of the nerves 

 going to the salivary gland and showed conclusively that the chorda 

 tympani was secretomotor to the submaxillary gland. He also 

 showed that in many cases the gland could secrete against a pres- 

 sure greater than the arterial pressure and indeed that secretion 

 could continue even when the circulation to the gland was arrested, 

 thus disproving Haller's ultrafiltration theory. Ludwig's approach 

 to physiological problems had a sophistication that set him apart 

 from his contemporaries and he was the first man to attempt to 

 apply exact measurement and physical rigour to physiological 

 problems. Ludwig's genius soon became absorbed in other 

 branches of physiology, but the torch was taken up by Claude 

 Bernard, probably the greatest physiologist of the nineteenth 

 century. 



Bernard became interested in salivary secretion early in his 

 career and sustained this interest until nearly the end. In the lec- 

 tures given at the College de France in 1856 (Bernard, 1856) he 

 collected together a wonderful amount of precise, careful observa- 

 tion and experimentation on the salivary glands. This included a 

 detailed study of the chemistry of the saliva from the different 

 glands collected under a great variety of circumstances, as well as 

 studies on salivary proteins using the novel methods of salting out 

 with sodium sulphate and magnesium sulphate; he also investi- 

 gated the distribution of amylase in different species. In a study of 

 the total saliva secreted by the minor as well as the major salivary 

 glands, he revived and improved the methods of production of 

 salivary fistulae and introduced the important technique of sham 

 feeding, using an oesophageal fistula. 



It was an investigation of the thirst that develops with salivary 

 fistulae that led him not only to a clear appreciation of the moisten- 

 ing and lubricating function of the saliva, but also to the realiza- 

 tion that the sensation of thirst was not a peripheral one due to 

 deficient moistening of the mouth but rather to the effects of 

 systemic dehydration. He describes how he arrived at this con- 

 clusion thus: "It is not necessary to believe that the excessive 

 thirst after a parotid fistula is due to a great dryness of the pharynx 



