474 6. HELODERMATIDJE 



In northern Sonora, it has been collected at Guadalupe 

 Canyon, San Bernardino, Niggerhead Mountain, and San 

 Pedro Bay. 



Habits. The Helodermas are the only lizards whose 

 bite is known to be poisonous. The venom is secreted by 

 large glands situated just under the chin, and flows out, onto 

 the floor of the mouth, between the lips and the gums. Be- 

 ing below the teeth and not directly communicated to them, 

 the poison sometimes fails to find its way into a wound 

 although the teeth are grooved to afford it a passage. The 

 upper jaw of the Monster is provided with a saliva which 

 possesses no poisonous properties. This harmless saliva 

 appears to be present in the lower jaw as well as in the up- 

 per, but is there mixed with venom about as deadly as that 

 of the rattlesnakes. Although provided with so powerful 

 a poison, the Gila Monster is so gentle and sluggish that it 

 is not always easy to cause one to bite, but when thoroughly 

 angered it bites fiercely, throwing its head to one side with 

 lightning-like quickness, and holding like a bull-dog to 

 whatever it has seized. Sumichrast says that the Mexican 

 species turns onto its back before biting. Although this 

 observation has not been confirmed, the presence of venom 

 in the lower jaw only would explain such an action. 



The more important conclusions regarding the physio- 

 logical action of the poison are summarized as follows:* 



1. The effects of Gila Monster poison differ in no 

 important respect from those of various snake venoms. 



2. The poison appears to act directly upon the respira- 

 tory center, causing a quickening and then a gradual paraly- 

 sis of respiration. 



3. The heart also exhibits a period of increased activity 



*Van Denburgh & Wight. Amer. Jour. PhysioL.Vol. IV. No. V, Sept. I, 1900, p* 237* 



