52 THE VENOM OF HELODERMA. 



Van Denburgh (Trans. Am. Phil. Soc, vol. 19, 1898, p. 199) and Van 

 Denburgh and Wight (Am. Jour. Phys., vol. 4, 1900, p. 209) collected the 

 secretion either by causing the helodermas to chew filter paper or to bite on 

 rubber. They made observations on the physiological effects of the venom 

 upon dogs, cats, and frogs, and also a few experiments to test its effect upon the 

 red blood-corpuscles. 



We have studied the venom of both species in regard to its physiological 

 action, in its influence in causing hemolysis of red blood-cells, and in several 

 other ways. 



METHOD OF COLLECTING THE VENOM AND FACTORS WHICH 

 INFLUENCE THE AMOUNT OF SECRETION. 



A number of small ducts lead from the poison gland into a groove between 

 the lower lip and the teeth of the lower jaw. When the animal bites the secre- 

 tion gushes into this groove. The ducts open near the bases of the small 

 pointed teeth; consequently the venom is ejected in the neighborhood of the 

 several wounds made by the teeth, the grooves present on the outer side of the 

 teeth carrying the venom into the wound ; there is, however, no means by which 

 the Heloderma can inject venom directly into an enemy, as does the Crotalus. 



In order to collect the venom we caused the animals to bite upon a piece of 

 soft rubber and with a capillary pipette drew off the secretion from the lower 

 side of the rubber. This method of collecting has the double advantage of 

 yielding a maximum of the secretion and also secretion from the lower jaw 

 only. An animal in good condition will usually chew the rubber for several 

 minutes and each time the jaws close there is a gush of venom into the groove, 

 but the length of time which the chewing continues, as well as the amount of 

 secretion which flows out at each bite, is subject to great variations. Chief 

 among the factors which influence these variations are : 



(1) The condition of the teeth. The teeth are easily and frequently in- 

 j ured, and animals without teeth spit out the rubber as soon as it is placed in 

 the mouth. Probably the reason that animals with good teeth do not spit out 

 the rubber is that the teeth become caught in the rubber, which thus can not 

 be pushed out by the tongue. 



(2) The time which has elapsed since the previous collection. If the 

 secretion is taken every day the amount falls off rapidly, and even if the ani- 

 mals chew well the flow is quickly exhausted and may at times be absent 

 altogether. 



(3) The nutritive condition of the animal. We found that animals which 

 had not eaten food for some time yielded little or no secretion, but that soon 

 after they began to take food again the secretion became abundant. 



Besides these factors it seems that the temperature and the length of time 

 since the last feeding also play a role, but the evidence on these heads is not 

 sufficient to enable us to draw definite conclusions. It is also probable that 

 when animals are kept for a considerable length of time in captivity they grad- 

 ually lose the power of secreting venom. 



