319 



but not necessarily in the rest of its extent ; 3. That the track os- 

 sifies when abscess ensues, or when it becomes fistulous ; and 4. 

 That balls and foreig'n bodies are always enclosed in a mass of 

 ossified pulp. This ossified pulp, when examined in thin sec- 

 tions under the microscope, presents a formation identical with 

 the irregular ivory which fills the pulp cavity of the tusks of the 

 walrus, and the tusk of the cetacea, and consists of anastomosing 

 Haversian canals, secondary medullary canals, and wavy bundles 

 of Retzian tubes. These canals and tubes are situate in a clear 

 matrix, in which there are occasional patches of coarse cells, 

 through the medium of which the bundles of Retzian tubes com- 

 municate with one another, and with the tubes of the regular 

 ivory. The formation of the irregular ivory which surrounds 

 wounds, abscesses, and foreign bodies in the pulp, does not pro- 

 ceed indefinitely, but is limited by the closing up of the orifices 

 of the Haversian canals, and the consequent separation of their 

 contained ramifying pulp from the general system. The irregular 

 ivory is then, in reference to the general pulp of the tusk, in the 

 same relation as the regular ivory, and at length becomes enclosed 

 in the latter by the transformation of the pulp on its surface. It 

 was then stated that foreign bodies enter the pulp in three ways ; 



1. Through the base of the pulp, without wounding the ivory; 2. 

 Through the free portion of the ivory ; and 3. Through the sides 

 of the socket. A case of the first kind is described by Mr Combe 

 in the Philosophical Transactions. Wounds of the second kind, 

 when there is no trace of the track of the ball, have, with the ex- 

 ception of the formation of the irregular ivory, been sufficiently 

 explained by former authors. In reference to wounds of the third 

 kind, Mr Goodsir demonstrated that cicatrices, partial and com- 

 plete, do occur, and that they are produced by the plugging up of 

 the hole from within by irregular ivory or ossified pulp, and from 

 without by cement formed by the membrane of the follicle. In 

 conclusion, it was stated that every case of wound, fracture, and 

 enclosureof foreign bodies in ivory, might be explained by the 

 facts, that a tusk was an organ of double growth, and that its 

 follicle played an important part in the healing of wounds through 

 the socket. 



2. On the Theory of Waves. Part II. By Professor Kelland. 



The present memoir is a continuation of that which the author 

 presented to the Society in April 1839. It is divided into four 

 sections. In the first (which is marked Section 4, in continuation 



