If this law be not observed, intellectual activity may be gratified, self-conceit or love of novelty and excitement may be pandered to, the panic of fear in human beings may be worked upon, but the attainment of scientific truth in biology will be impossible. It is thus seen that methods of biological research which involve cruel or destructive experimentation are both ethically unjustifiable and intellectually fallacious. They are unscientific methods which will inevitably be abandoned as we attain to clearer views of that unity of truth in which the reconciliation of human conscience with intellectual activity becomes alone recognised as science. CHAPTER X _Rational Experiment in Research_ As an illustration of legitimate and even heroic experiment, the trial made with cholera bacilli by Dr. Von Pettenkofer of Munich on himself during the cholera epidemic of 1891 deserves permanent record.[19] It is of importance as showing the fallacy that may be involved in the exaggerated search for bacilli, as the chief cause of disease, which is the favourite theory and practice of the present day. Dr. Von Pettenkofer (in opposition to the common medical belief) asserts that the diffusion of the cholera germ or cholera bacillus is not the chief cause of cholera. He states that there are two other absolutely necessary conditions, without which no outbreak of cholera is possible, and if these conditions are not present, the cholera germ may be breathed with no production of cholera. The first condition is the unhealthy state of the soil or locality. But even this does not produce an outbreak if the second condition does not exist--viz., individual predisposition; and he shows that neither the cholera germ nor the insanitary locality, nor both combined, will produce cholera if this individual predisposition does not exist. He further states that no experiments upon the lower animals can be relied on; the only _proof_ in relation to cholera must be from the experience of human beings.