6o COMPARATIVE PHYSIOLOGY 



substances analogous to or antagonistic to the effects of the 

 poison in the blood itself. The supersensitivity in the one case 

 and increased resistance in the other in part reside in the cells 

 of the organ affected. Thus Dale (19 12) has shown that the 

 isolated virgin interns of the guinea pig from an animal treated 

 with horse serum as the anaphylactic reagent shows specific 

 supersensitiveness to the reagent. Again, Gunn and Heath- 

 cote (1921) have shown the greater resistance of the cat as 

 compared with the rabbit to cobra venom is shown by isolated 

 organs of the two species. The minimal lethal dose per 

 kilo of cobra venom for the cat is twenty times that for the 

 rabbit. Both the isolated heart and gut muscle of the cat 

 can withstand much higher doses of cobra venom than corre- 

 sponding preparations from the rabbit. Of the venoms of 

 Arthropods the most important are those of the spiders, scor- 

 pions, and hymenoptera. Nearly all spiders possess poison 

 glands connected with the mouth parts, the poison being 

 instantly fatal to the small animals on which they prey. The 

 toxin is destroyed by heat, and like the venom of viperine snakes 

 displays both coagulant and haemolytic properties with refer- 

 ence to vertebrate blood. Scorpion venom more closely re- 

 sembles the venom of the Colubrine snakes {vide infra). The 

 poison glands of bees contain at least three toxic substances, 

 one of which possesses haemol3^ic properties and acts on the 

 nerve centres, but like viperine venom produces marked local 

 effects. A particularly interesting case from the pharmaco- 

 logical standpoint is the presence of a substance allied to 

 tyramine (parahydroxyphenylethylamine) in the salivary secre- 

 tion of the cephalopod (Henze). By means of it the cuttle- 

 fish paralyses its decapod prey. Tyramine is closely related 

 to tyrosine, as is the latter to the melanic secretion of the ink 

 sac in cephalopods. It is one of a class of compounds allied 

 to " adrenaline," the hormone of the mammalian suprarenal 

 glands, prepared synthetically by Barger and Dale. Adrena- 

 line itself has been isolated by Abel and Macht in association 

 with an alkaloid bufagin having an action akin to digitalis in 

 the poisonous parotid and skin glands of the toad, Bufo agua. 

 The venoms of snakes may be divided into two groups. 



