64 VIPERAD^E. 



Philosophical Transactions for 1818. This tube, although 

 completely enclosed, excepting at its basal and apical 

 orifices, must be considered as formed merely by the 

 closing round of a groove in the external part of the tooth 

 itself, and hence not in any way connected with the inner 

 cavity of the tooth, in which exists the pulp upon which 

 the substance of the tooth is formed. The base of the 

 tooth, and consequently the basal orifice of the tube just 

 described, is embedded in a sac, into which the poison is 

 poured from the ducts of the glandular structure by which 

 it is secreted, and which is believed to represent the 

 parotid gland of the higher vertebrata. The poisonous 

 fluid itself is inodorous, tasteless, and of a yellow colour. 

 It is secreted in greater quantity, and its qualities are 

 more virulent in a high temperature than in cold. Its 

 secretion may be greatly increased by local irritation ; as 

 is evidenced by the following fact. Some years since I 

 was dissecting very carefully and minutely the poison 

 apparatus of a large Rattlesnake, which had been dead 

 for some hours ; the head had been taken off immediately 

 after death; yet as I continued my dissection the yellow 

 poison continued to be secreted so fast as to require to be 

 occasionally dried off with a bit of rag or sponge ; I be- 

 lieve that there could not have been less altogether than six 

 or eight drops at the least. 



When the animal inflicts the wound, the pressure on the 

 tooth forces a small drop of the poison through the tube ; 

 it passes through the external orifice, which is situated on 

 the concave side of the curved tooth, and is in the form of 

 a slit. The manner in which the blow is inflicted is as 

 follows. The animal generally throws itself in the first 

 place into a coil more or less close, and the anterior part 

 of the body is raised. The neck is bent somewhat abruptly 



