Not bad air, not just a weakness of the infected human body’s immune system, not any of the myriad theories that had filled the puzzled heads of his audience all of their working lives...but a bacterium. Not just a bacte- rium, but a bacillus the like of which had never been even suspected be- fore, a most singular life form, with a frightening propensity to infect every cat and chicken, pigeon and guinea pig, the white mice and rats, oxen and even two marmosets, into which Koch had injected it.
The Forgotten Plague: How the War against Tuberculosis was Won - and Lost Frank Ryan, 1992
The book De Morbus Contagiosus, written in 1546 by Girolamo Fracastoro (1478-1553), explained the contagious nature of TB. He pointed out that bed sheets and clothing could contain contagious particles that were able to survive for up to two years. The word “particles” may have alluded to chemicals rather than to any kind of living entity.
In his publication A New Theory of Consumptions, in 1720, the English physician
Benjamin Marten (1704-1722) was the first to conjecture that TB could be caused
by “minute living creatures", which, once they had gained entry to the body, could generate the lesions and symptoms of phthisis. He further stated, that consumption may be caught by a sound person by lying in the same bed, eating and drinking or by talking together so close to each other as to “draw in part of the breath a con- sumptive patient emits from the lungs”.
In 1865, the French military doctor Jean-Antoine Villemin (1827-1892) demon- strated that consumption could be passed from humans to cattle, and from cattle to rabbits. On the basis of this revolutionary evidence, he postulated that a specific microorganism caused the disease. At this time William Budd (1811-1880) also concluded from his epidemiological studies that TB was spread through society by specific germs.
On the evening of March 24, 1882, in Berlin, before a skeptical audience composed of Germany's most prominent men of science from the Physiological Society, Rob-
ert Koch (1843-1910) (www.tuberculosistextbook.com/link.php?id=2) made his famous presentation Die Aetiologie der Tuberculose. Using solid media made of potato and agar, Koch invented new methods of obtaining pure cultures of bacteria. His colleague Julius Richard Petri (1852-1921) developed special flat dishes (Petri dishes), which are still in common use, to keep the cultures. Koch also de-
1.4. The discovery of the tubercle bacillus 33 veloped new methods for staining bacteria, based on methylene blue, a dye devel- oped by Paul Ehrlich (1854-1915) (www.tuberculosistextbook.com/link.php?id=3), and counterstained with vesuvin. "Under the microscope the structures of the animal tissues, such as the nucleus and its breakdown products are brown, while the tubercle bacteria are a beautiful blue", he wrote in the paper that followed his dramatic presentation that March evening (Koch 1882).
He had brought his entire laboratory with him: his microscopes, test tubes, small flasks with cultures, and slides of human and animal tissues preserved in alcohol. Showing the presence of the bacillus was not enough. He wanted his audience to note that bacteria were always present in TB infections and could be grown on solidified serum slants, first appearing to the naked eye in the second week. Then, he showed that, by inoculating guinea pigs with tuberculous material obtained from lungs, intestines, scrofula or brains of people and cattle that have died from TB, the disease that developed was the same, and cultures obtained from the experimental animals were identical on the serum slopes. Koch continued his speech, proving that whatever the dose and/or route he used, no matter what animal species he in- oculated, the results were always the same. The animals subsequently developed the typical features of TB. He concluded saying that “…the bacilli present in tu- berculous lesions do not only accompany tuberculosis, but rather cause it. These bacilli are the true agents of tuberculosis” (Kaufmann 2005).
Koch fulfilled the major prerequisites for defining a contagious disease that had, in fact, been proposed by his former mentor Jacob Henle (1809-1885). The re- knowned Koch's postulates (or Henle-Koch postulates) were then formulated by Robert Koch and Friedrich Loeffler (1852-1915) in 1884, and finally polished and published by Koch in 1890. The postulates consist of four criteria designed to es- tablish a causal relationship between a causative microbe and a disease:
• The organism must be found in all animals suffering from the disease, but not in healthy animals
• The organism must be isolated from a diseased animal and grown in pure culture
• The cultured organism should cause disease when introduced into a healthy animal
• The organism must be re-isolated from the experimentally infected animal. In 1890, at the 10th International Congress of Medicine held in Berlin, Koch an-
34 History
when given both pre- and post-exposure. It was called 'tuberculin' and was prepared from glycerol extracts of liquid cultures of tubercle bacilli. Clinical trials using tuberculin as a therapeutic vaccine were soon initiated. The results were published in 1891 and revealed that only few persons were cured, at a rate not different from that of untreated patients. But, although results for treatment were disappointing, tuberculin was proven valuable for the diagnosis of TB (Kaufmann 2005).
One of Koch’s papers (Koch 1891), describing the preparation and partial purifica- tion of tuberculin served as the first description of the productionof the partially purified derivative (PPD) of tuberculin, presently used in the Mantoux test, also known as the Tuberculin Skin Test, Pirquet test, or PPD test (see Chapter 13).