MR GOODSIR ON MUSKET-BULLETS FOUND IN THE TUSKS OF THE ELEPHANT. 97 



the same relation as the whole internal surface of the irregular ivory of the tusk. 

 The pulp, therefore, becomes converted into ivory, not only on the whole internal 

 surface of the tusk, but also on the surface of the newly-formed mass. The cause 

 of the formation of the irregular ivory to a limited extent only, when it exists as an 

 abnormal structure, I have not been able to ascertain ; but its mode of develop- 

 ment and limitation is highly interesting, and forms a leading distinction between 

 a tooth and a true bone under similar circumstances. 



From this description it is evident that the abnormal ivory in the elephant's 

 tusk strongly resembles, if it be not identical with, the peculiar substance which 

 fills the pulp-cavities of the tusks of the walrus and the teeth of the cetacea, first 

 announced as a distinct species of dentar tissue in a paper read before this So- 

 ciety five years ago by Dr KNOX, and since minutely described by RETZIUS, OWEN, 

 and ALEXANDER NASMYTH.* 



This identity of a diseased structure in one animal with a normal structure 

 in another is remarkable, and must be looked upon as another instance indicating 

 the existence of a system of laws regulating the relations between healthy and 

 morbid tissues ; laws which have been speculated upon, but have never been 

 sufficiently investigated by anatomists. 



Having now given the anatomical characters of the abnormal ivory which 

 invariably surrounds musket-bullets and other foreign bodies which lodge in the 

 pulps of the tusks of the elephant, I shall proceed to state the various conditions 

 under which these enter the organ, and the changes which ensue. 



Foreign bodies enter the tusk in three ways : First, through the free portion 

 of the tusk ; secondly, through that part of the organ which is contained in the 

 socket ; and, thirdly, from above through the base of the pulp. 



First, When the ball hits the free portion of the tusk, if it only penetrates to 

 a certain depth of the ivory, no change whatsoever can take place. Neither the 

 cement nor the ivory can be reproduced. In course of time the hole may be obli- 

 terated, the ball may be got rid of by wearing down of the ivory, and the ivory 



* CUVIER described this species of dental tissue in the tusk of the walrus, and compared it to pud- 

 ding-stone. Dr KNOX, in the paper to which I have referred in the text, affirmed that, in addition to 

 the cement, enamel, and ivory, a fourth substance, namely, the substance described by CUVIER, entered 

 into the formation of many teeth. He stated that, in the teeth of certain fishes, this substance, or a 

 tissue closely allied to it, constituted the greater part of their mass ; the other three elements having 

 disappeared or become greatly diminished in bulk or importance. RETZIUS has accurately described the 

 microscopic structure of this class of dental substances, as existing in different animals. Mr OWEN has 

 extended and confirmed the observations of RETZIUS. Lastly, to Mr A. NASMYTH belongs the merit of 

 having pointed out the resemblance which this kind of substance (which he denominates ossified pulp) 

 bears to diseased ivory in the tusks of the elephant, and still more closely to the substance which fills 

 the pulp cavity of the aged human tooth. In ignorance of Dr KNOX'S previous observations, he announced 

 this kind of ivory as a fourth dental substance. 



VOL. XV. PABT I. D d 



