472 Royal Society : — 



examined, it will be found that one of two actions has been set up. 

 Either additional cementum will have been developed upon the 

 surface of the fang, or its bulk will have become diminished by 

 absorption. Similar conditions supervene when the crown of a tooth 

 has been lost by caries. 



In old persons we find the teeth are lost without apparent disease 

 in the dental tissues. The teeth become loose and fall out, the roots 

 being in such cases translucent like horn. This condition is the 

 result of consolidation of the dentinal fibrils, and is followed by 

 absorption of the cementum and dentine. Cases may be found in 

 which the whole of the fang has been absorbed, but reduction ,ta 

 two-thirds or half of the normal bulk is very common. ...ill 



The concurrence of the foregoing changes m the sensibiHty of the 

 tooth, with the destruction or consolidation of the dentinal fibrils, 

 will, the author considers, justify the conclusion, that the dentinal 

 fibrils, in a state of integrity, are necessary to the normal condition 

 of dentine. q 



April 10. — Col. Sabine, R.A., V.P. and Treasurer, in the Chair^^ 



The following communications were read : — 



"Account of 'Experiments on the Vagus and Spinal Accessory 

 Nerves." By Augustus Waller, M.D., F.R.S. 



The important functions of the organs more or less completely 

 dependent for their innervation on the vagus nerve, have afforded the 

 reason of so many attempts by previous physiologists to determine 

 the exact influence exerted by the fibres arising from different 

 sources which are intimately blended together in the trunk of the 

 mixed vagus. Since Sir Charles Bell's discovery of the different func- 

 tions of the anterior and posterior roots of the spinal pairs, it has 

 become still more important to determine how far the same law holds 

 good with regard to the vagus nerve, and whether at its origin, it is 

 a purely sensory nerve, receiving its motor fibres from the internal 

 branch of the spinal accessory and perhaps from other sources. Ac- 

 cording to Bischoff and Longet, the vagus at its origin and as far as the 

 upper ganglion, is purely sensory, and becomes possessed of motor 

 power from its junction with the internal branch of the accessory, and 

 from other branches derived from motor nerves (Longet). The obser- 

 vations of Bernard have led him on the contrary to adopt the opinion, 

 that the vagus at its origin is a mixed nerve ; because after destroying 

 the spinal accessory, no effect on the functions of the heart, stomach, 

 or lungs was observed, and the only organs visibly dependent on the 

 spinal accessory were the larynx and pharynx. After bearing testi- 

 mony to the correctness of the observations made by Bernard with 

 regard to the effects immediately following destruction of the spinal 

 accessory, the author considered it desirable to apply to the determina- 

 tion of this question his new means of investigation, in addition to 

 those previously employed. His first observations on the vagus, 

 published in the * Comptes Rendus ' of the Academic des Sciences, 

 1852, had already led him to entertain the idea, that the vagus proper 

 was a purely sensory nerve. They first consisted in cutting this nerve 



