4 Historical Introduction 



fairly convincing evidence of this in the case of the vagus and the 

 stomach. Indeed the idea of nervous control of secretion rapidly 

 became accepted and we can only be surprised that it was not until 

 1 85 1 that Ludwig proved experimentally the existence of nervous 

 control of salivary secretion. 



In this same period the science of biochemistry was arising. 

 Tiedemann and Gmelin's book entitled Physiological and chemical 

 experiments in digestion (1826) was one of the pioneers of biochem- 

 istrv. Thanks to Berzelius methods of analysis had been greatly 

 improved, and Tiedemann and Gmelin were to advance these 

 methods further and apply them with remarkable skill and vision 

 to the analysis of saliva and the other digestive juices. They had the 

 perspicacity to realize that results obtained on the saliva obtained 

 from the parotid duct in the dog might be superior for analytical 

 purposes to the more heterogeneous mouth (mixed) saliva. It is 

 regrettable that many contemporary workers have still to learn this 

 lesson. Amongst many observations they proved that the red colour 

 given by human saliva with ferric chloride (noted by Treviranus) 

 was due to the presence of thiocyanic acid which had recently been 

 discovered by Porett. They isolated the thiocyanic acid by extrac- 

 tion of thiocyanates from dried saliva with alcohol and distillation 

 of the free acid whose constitution was established by oxidation to 

 sulphate identified by precipitation as barium sulphate. They also 

 showed that the major cation of saliva was potassium (identified as 

 potassium sulphate and potassium chlorplatinate), that saliva was 

 alkaline, and that there were traces of a phosphorus containing fat 

 in it. They made a thorough study of the proteins of saliva, and 

 showed that acetic acid precipitated mucin from saliva as a soft 

 transparent mass. They also found that after crushed oats had 

 been mixed with sheep saliva and left for a while they would no 

 longer give a blue colour with iodine. This appears to be the first 

 description of salivary amylase. 



The new methods of analysis developed by Tiedemann and 

 Gmelin were soon applied by Mitscherlich (1832) to the study of a 

 case of parotid fistula in man. In a delightful paper Mitscherlich 

 described the development of the parotid fistula and the circum- 

 stances under which the secretory rate changed, these included the 

 effects of diet, mastication and sleep. He also compared the fistula 

 saliva with mouth saliva. Mitscherlich was very impressed with the 

 rapidity with which the saliva flow rate changed with such stimu- 



