3 3 2 THE POPULAR SCIENCE MONTHLY. 



belladonna leaves (Atropa belladonna, deadly nightshade). You 

 may feed them with belladonna for weeks without observing 

 the least toxic symptoms. The meat of such animals, however, 

 proves poisonous to any one who eats it, producing the same 

 symptoms as the plant. Pigeons and various other herbivora are 

 also to some degree safe from the effects of this poison, while in 

 warm-blooded carnivora it causes paralysis and asphyxia. In 

 frogs the effect is a different one, consisting of spasms. The meat 

 of goats which had fed on hemlock has sometimes occasioned 

 poisonous effects. Chickens are nearly hardy against nux vom- 

 ica and the extremely dangerous alkaloid, strychnine, contained 

 in it, while in the smallest amount it is a fatal poison to rodents. 

 More remarkable yet in this respect is the immunity of Choloepus 

 Hoffmanni, a kind of sloth, living on the island of Ceylon, which, 

 when given ten grains of strychnine, was not much affected. 

 Pigeons are possessed of high immunity from morphine, the chief 

 alkaloid of opium, as well as from belladonna. Eight grains 

 were required to kill a pigeon, not much less than the mortal dose 

 for a man. Cats are extremely sensitive to foxglove (Digitalis 

 purpurea), which on the contrary may be given to rabbits and 

 various birds in pretty large doses. Many kinds of fish may be 

 killed by just a trace of Cocculus indicus, although their meat is 

 not made injurious by it. Laughing-gas, or nitrogen monoxide, 

 a means used to relieve pain in light surgical operations, affects 

 man more than any other creature ; when breathed in a mixture 

 of four parts of laughing-gas and one part of oxygen it produces 

 a pleasant kind of intoxication together with diminished sensi- 

 bility, though in animals no such effect has been observed. 



The immunity of certain animals against the bite of venomous 

 serpents is remarkable. Numerous observations have been re- 

 corded proving the polecat, hedgehog, and buzzard to be proof 

 against the bite of the viper ; it is mortal for most other animals 

 of the same size and nearly related to them. 



Immunity, however, is not limited to the relations of animals 

 to poisons of vegetable or animal origin, but is manifested as 

 well in conditions and processes in the healthy animal organism 

 and in its susceptibility to diseases. The resistance offered by 

 the living stomach of an animal to the dissolving effect of the 

 juice secreted by the stomach itself has to be explained by im- 

 munity. A watery solution of pepsin the digestive principle of 

 the stomach acidulated by muriatic acid, and thus, as to compo- 

 sition, corresponding to the digesting juice of living animals, upon 

 addition of pieces of the stomach of any mammal, dissolves them, 

 forming a perfect solution. The stomach of the living healthy 

 animal, on the contrary, does not undergo the least change by 

 the secreted juice ; it is proof against the digesting effect of its 



