216 BACKBONED ANIMALS. 
of the Southern and Western States attains a length of 
three feet, and is so fragile that the slightest blow severs 
. it in sections. The 
upper surface is 
yellowish green 
spotted with 
black. 
Heloderma 
( Helodermida). — 
The “Gila mon- 
ster,” or Heloder- 
ma (Fig. 261), is 
the largest lizard 
of North America, 
attaining a length 
of three feet, and enjoying the distinction of being the only 
poisonous member of the order. In appearance they are 
repulsive, being covered with scales, the whole resembling a 
flinty, faceted armor. The general color is black, marked 
with yellowish-orange or white interspaces. The tail is 
cylindrical and clumsy. Their movements are slow and 
uncertain, resembling those of a young alligator. The 
teeth are fissured, and at the bases of the grooves are the 
ducts from which the poisonous saliva passes into the 
wound.* After biting, the heloderma appears sluggish, 
Fic. 260.—Glass snake (Of/isaurus ventralis). 
* According to Mitchell and Reichert, the physiological action of 
the poison is quite different from that of snake-poison. The latter 
kills by paralyzing the respiratory center, while the poison of the helo- 
derma paralyzes the heart. When injected subcutaneously it causes no 
local injury, the effect being to arrest the motion of the heart, which 
slowly becomes contracted, and the spinal cord paralyzed. It is not 
necessarily fatal to human beings, though an American scientist, after 
being bitten, was barely able to call assistance. In experiments tried 
by Sir John Lubbock, a live frog when bitten died almost immediately 
in convulsions. A Guinea-pig, bitten in the hind-leg, died in three 
minutes, and young rats succumbed even more quickly. The specimen 
kept in the New York Zoélogical Garden thrived upon hard-boiled eggs. 
