The life of any creature, man, animal or plant, is one long fight against being poisoned. The poisons get us in all sorts of ways. Some, like strong acids and caustics, actually destroy the flesh, just as they would eat a hole thru the top of a stove, and we are crippled or die for lack of a lining to our stomachs. A great many poisons, like alcohol, ether, chloroform, the various alkaloids, such as strychnin and atropin and cocain, which we use as medicines, and nicotin, which is the alkaloid of tobacco, the poisons of many toadstools, caffein (don’t call it caf-een, but caf-fe-in, like co-ca-in) which we get in tea and coffee (and therefore ought not to drink either till we are quite grown up) and half a thousand others, mostly with names ending with “in” and the ptomains (again it’s three syllables, to-ma-in) which form in fish and ice-cream that have been kept too long, and poison whole families at once, all these do not do any special harm in the stomach. But when they get into the blood stream, they go straight for the nerves and upset them. Ether, chloroform, and cocain, as we all know, begin by paralysing the pain nerves. The pain sense is cut off from the brain, so that no matter how much damage is being done, we don’t know anything about it. And a mighty good thing it often is that we don’t!

Other poisons attack the blood. The fumes from burning charcoal and some sorts of gas that we use for lighting and cooking, lock the oxygen of the air so tightly to the red blood corpuscles that are carrying it to the cells, that the cells cannot get it away from them. So the tissues die from lack of air, tho there is plenty and to spare in the lungs and the blood—only the blood hangs onto it, and the rest of the body cannot pry it loose. Snake poisons, also, kill by attacking the blood, thus cutting off the supply of air. These dissolve the blood corpuscles that carry the oxygen, and literally “turn the blood to water.” Then the blood, having no corpuscles, cannot carry oxygen to the cells of the body, and the body dies of suffocation, tho the lungs take as much air as before. Snake venom, therefore, does not do the least harm in the mouth or stomach. One can suck the poison from the wound made by the snake’s teeth, and spit out the poisoned blood, or even swallow some of it, without the least danger. One could wash himself in rattlesnake poison, and take no harm, so long as he kept a whole skin so that nothing got into his blood.

Perhaps you know that pigs are the great enemies of rattlesnakes, killing them and eating them up as if the serpents were so many apple parings. The rattlesnakes bite the pigs. But the pig’s skin is thick, and under it is a great layer of fat, in which there is almost no blood. So when the pig gets a dose of poison under his skin, enough to kill two or three men, he does not mind it at all. The venom, shut up in the fat, works out into the blood so slowly that the pig can make new blood corpuscles almost as fast as the poison destroys the old ones. So at the worst, the pig feels only a little discomfort. But the rattlesnake is safely tucked away in the pig’s inside, where it will never do any more biting.

What I want you to remember, then, is this: All living things are poisonous. We, ourselves, are continually manufacturing in our bodies carbon dioxid, sugar, ammonia, and a score of other things, any of which would soon put an end to us if we did not have a special machinery for getting rid of them before they get a chance. A great many plants produce also certain special poisons, strychnin, nicotin, and the like, which would kill them if they made too much. A few animals, too, like the snakes and some fishes and various insects, manufacture poisons, which also would kill them. In general, the blood of any animal is a poison to an animal of any other sort, and always a poison of the same sort as snake venom which does no harm in the stomach, but is fatal when enough is taken into the blood. In general, then, each creature has some means of getting rid of its own poisons, but the poisons of any different sort of creature will kill it.