VI PREFACE. 



in cases in which the heart and the blood vessels are diseased, may 

 become so pronounced as to render a certain amount of medical 

 skill necessary. Or if, to avoid such pain, it be deemed advisable 

 to administer anesthesia, then must the dentist be constantly 

 on his guard that no more than the proper amount of anesthetic 

 is given, which he can- do intelligently only by observing the 

 condition of the nervous and circulatory systems. 



Besides knowing something about the physiology of the body 

 as a whole, the dentist must be particularly familiar with the 

 local physiology of the mouth, such as the finely coordinated 

 nervous mechanisms involved in the acts of mastication and 

 swallowing and the secretion of saliva. He must understand 

 the nature of the sensations of the teeth and buccal mucosa, and 

 be on the lookout for any lesions of the cranial nerves that sup- 

 ply the muscles and other tissues adjacent to the mouth cavity. 



The chemistry of the saliva has demanded special attention 

 because of the very interesting scientific investigations which 

 are being prosecuted 'regarding the nature of the undoubted 

 relationship that exists between changes in the saliva and the in- 

 cidence of dental caries. To adequately describe the present 

 status of this work we have found it necessary to devote some 

 space (in the. second chapter) to a review of the main physico- 

 chemical principles which may regulate the reaction and neu- 

 tralizing power of saliva. 



Whenever the occasion presented itself to do so, we have given 

 a brief description of the general nature of the diseases in which 

 dental involvement is possible. 



A few simple, but very instructive, laboratory demonstrations 

 are described in an appendix at the close of the book. We have 

 found that such demonstrations furnish an invaluable aid in 

 the teaching of the subject. 



To facilitate a clear understanding of the subject, diagrams 

 have been used whenever necessary, and many of these have 

 been specially drawn for the work. To Prof. T. Wingate Todd 

 and Mr. P. M. Spuruey, the authors are deeply indebted for the 

 valuable assistance which they gave in the preparation of these. 



R. G. PEARCE. 

 J. J. R. MACLEOD. 



