COMMON VIPER. 61 



ing at its basal and apical orifices, must be considered as 

 formed merely by tlie closing round of a groove in tlie ex- 

 ternal part of the tootli 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 struc- 

 ture by which it is secreted, and which is believed to re- 

 present 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 irri- 

 tation ; 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 occasion- 

 ally dried off with a bit of rag or sponge ; I believe 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 backwards, and 

 the head fixed almost horizontally. In an instant the head is, 

 as it were, launched by a sudden effort towards the object of 

 its anger, and the erected tooth struck into it, and withdrawn 



