# Scientific Method in Biology/Chapter 10

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. 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.
The supremacy of sanitation is the lesson which is being gradually taught by such humane scientific experiments. Dirt in its largest sense as matter in the wrong place, whether in air, water, food, clothing, habitation, soil, or contact, is undoubtedly a main physical cause of disease.
But in all epidemic disease the emotion of fear ​must be recognised as a most potent predisposing cause. The great fact of mind or emotion is a powerful inﬂuence in producing, in preventing, or in curing disease.
This psychological side of medicine is only beginning to receive due attention. As the fallacies which arise in animal experimentation from the production of fear, pain, and coma have not yet been fully recognised, so the inevitable influence of mind in modifying physical conditions has never yet been studied scientifically in human medicine. Yet facts exist in unsuspected abundance which need to be collected, verified, tabulated, and their laws of action diligently studied.
It is known that even that strong muscle the heart may be ruptured by the agony of intense emotion. At Blackburn, the daughter of a woman charged with theft became dumb with horror at her mother's sudden arrest. Dr. Gayet, after vainly treating a very pronounced aneurism of the internal carotid artery, was proceeding to operate, when his patient suddenly recovered. Hydrophobia, cholera, and even small-pox, appear to have been caused by fear.
The extent to which even the so-called microbes ​of infectious diseases may be produced by fear acting on idiosyncrasy demands very serious investigation; for as it is now generally conceded that morbid micro-organisms do not exist ab ætero, it is essential to know by what unhealthy conditions the micro-organisms, or living particles that always surround us, become disease germs.
One of our most distinguished London physicians has full records of the following noteworthy case, which is given not as scientifically proved, but as indicating a line of research which it is folly to ignore or refuse to investigate.
This gentleman attended a patient some years ago in an attack of confluent small-pox under these remarkable circumstances: This patient had always exhibited a morbid horror of the disease, refusing to hear anything about it, or to allow it to be referred to in his presence. A friend on one occasion brought a very fine collection of anatomical plates to show him, sent over from France. Amongst them was a representation of confluent small-pox in a woman. No sooner had this gentleman beheld it than he cried, 'Take it away. I cannot look at it; it makes me ill!' The next day his son sent for the doctor to ​see his father, who had felt unwell ever since the shock of seeing the pathological plate. He was found suffering from the first symptoms of an illness which proved to be an attack of confluent small-pox. The most searching inquiry failed to discover any traces of the disease, either in the neighbourhood or in any connection whatever with the patient. The cause of this illness, one of the most severe cases the doctor had ever met with, remained a mystery.
It has become of vital importance to investigate 'how far the mental attitude determines or permits the onset of infectious disease.'