"Interspecies differences may lead to concluding that substances that are innocuous or beneficial in humans are harmful, and that substances that have insidious effects on humans are harmless. For example, penicillin is extremely poisonous to guinea pigs. Had penicillin been subjected to the routine animal tests, as new drugs presently are, it would never have been tried on humans."

“Those experiments that cannot be justified on scientific grounds can be no more justified than the frivolous killing and torturing of animals. In fact they are even less capable of justification, since such experiments block more fruitful uses of scientific resources.”

“Arguments to the effect that it is wrong to cause pain and suffering to animals are often rejected by claiming that animals simply do not suffer. … Ironically, it is precisely upon the assumption that animals do suffer from stress, fear, and pain in a manner similar to humans that the validity of much of animal experimentation rests. Few, if any, conditions are studied as widely in animals as are pain, stress, ulcers, fear, and anxiety.”

“Rats and mice, for example, tend spontaneously to develop a high incidence of tumors. This renders them unsuitable for detecting tumors. Still, no animals are used as often as rats and mice for assessing the effect of numerous experimental treatments upon the production of tumors. The reason is that they are inexpensive and take up little room.”

“One type of medical research involves ascertaining whether certain pathological conditions in humans can be alleviated or cured by certain drugs. Animals are used as "models" upon which to test these treatments. To do this it is necessary for the animal subject to have the condition in question, and in order to bring this about healthy animals are made sick. … It turns out, however, that the conditions artificially induced have little in common with the naturally occurring diseases in animals and much less in common with the diseases in man.”

“The error in depicting critics of animal experiments as anti-science becomes clear when one begins to question the extent to which the purported scientific aims of these experiments are actually accomplished. For then it turns out that the experiments and not their critics are unscientific.”