28 PATHOGENIC BACTERIA. only been perfected by workers as it has been found nec- essary from time to time to comply in the most minute detail with Henle's conditions, and as, one point being carried, it was found necessary to advance on others. The first of these was that a specific organism should always be associated with the disease under consideration. As such presence, however, might be accidental, these organisms were not only to be found in pus, etc., but actu- ally in the living body. As they might be, even then, merely parasitic, and not associated directly with the causation of the disease, it would be necessary to isolate the germs, the contagium organisms, and the contagium fluids, and to experiment with these separately with special reference to their power of producing similar diseases in other animals. We now know that it has only been by strict compliance with all these conditions, again postulated by Koch, that the most brilliant scien- tific observers and experimentalists in Germany, France, England, [and America] have been able to determine the causal connection between micro-organisms and disease." 1 The refined methods of Pasteur, but more especially of Koch, by making possible the fulfilment of the pos- tulates of Henle caused an enormous increase in the rapidity with which data upon disease-germs were gath- ered. Almost within a decade the causes of the most important specific diseases were isolated and cultivated. In 1879, Hausen announced the discovery of bacilli in the cells of leprous nodules. The same year Neisser discovered the gonococcus to be specific for gonorrhea. In 1880 the bacillus of typhoid fever was first observed by Eberth, and independently by Koch. In 1880, Pasteur published his work upon " chicken- cholera. n In the same year Sternberg described the pneumococcus, calling it the micrococcus Pasteuri. In 1882, Koch made himself immortal by his discov- ery of and work upon the tubercle bacillus. The same 1 Woodhead : Bacteria and their Products, p. 65.