548 THE HISTORY OF BIOLOGY 



apparatus, constructed to his order by the physicist Abbe, of Jena — nowa- 

 days an indispensable aid to all who work with strong magnifications. 



Koch's first discoveries won him immediate fame; he was elected a mem- 

 ber of the Kaiserliches Gesundheitsamt in Berlin, whose leading force he 

 at once became, and had munificent sums placed at his disposal. During the 

 period that followed, he was responsible for two great achievements — the 

 discovery of the tubercular bacillus and the cholera microbe. In the case 

 of the former he tried to produce a specific cure in tuberculin, but, as is well 

 known, without success. Extremely valuable, on the other hand, was his 

 reform of the technics of disinfection : the abolition of the earlier ineffective 

 means of disinfection, such as fumigating with sulphur, and spraying with 

 carbolic, and the substitution of new experimentally tested and therefore 

 effective methods. 



Koch' s pupils 

 Koch's activities included also the training of a host of pupils; from all 

 countries there flocked to his laboratory students, who have since diffused 

 his methods everywhere. Among these may be named F. J. S. Loffler (born 

 in 1851), the discoverer of the microbes of diphtheria and swine-fever, and 

 Emil Behring (1854-1917), professor at Marburg, the founder of serum 

 therapy. In his later years Koch himself was the accepted authority on 

 everything concerning problems of infection, and he undertook many voy- 

 ages, especially to the tropics, with a view to investigate infectious diseases 

 existing there and to try to find a cure for them. Of a despotic disposition 

 and spoiled by his early successes, during his last years he did not always 

 take into account the most recent discoveries, nor who had made them, 

 which sometimes resulted in disputes that proved of little benefit for the 

 advancement of science. He laboured, however, up to the last, in spite of 

 impaired health; he died in 1910 of paralysis of the heart. 



While thus the disease-producing micro-organisms were giving rise to 

 an entirely new branch of research, the yeast-fungi, which were allied to 

 them, likewise became the object of close study. The pioneer in this field, 

 next to Pasteur, was the Dane Emil Kristian Hansen (1841-1909). Born of 

 a working-class family, he became at first a secondary-school teacher, ma- 

 triculated when he was near the age of thirty, and afterwards applied himself 

 to the study of chemistry and biology. When the famous Karlsberg laboratory 

 was instituted by the brewer Jacobsen, of Copenhagen, Hansen became its 

 leading force, and, in compliance with the wishes of the founder, devoted 

 himself entirely to the study of the fermenting process. In this sphere he 

 created what has ever since been the accepted technology of the subject; 

 in particular, he perfected the pure cultivation of the yeast-fungi by an in- 

 genious method of isolating a single specimen of these organisms, which 

 occur in masses and are only visible under the strongest magnifications; by 



