MODERNBIOLOGY 5 47 



safely isolating the micro-organisms that were to be examined and thus 

 obtaining pure cultures of them. He had certainly adhered to the idea of 

 constancy of species in the micro-organisms, but other investigators of the 

 highest reputation had maintained in contrast thereto the "pleomorphism" 

 of these beings — that one form could pass unrestrictedly into others of an 

 entirely different nature; this had been the view of Lister, the famous in- 

 ventor of the antiseptic bandage, as also of the well-known botanist Nageli, 

 for reasons which will be mentioned later on. It was in these circumstances 

 that Koch made his important contribution to the development of bacteri- 

 ology. 



Heinrich Hermann Robert Koch was born in 1843, the son of a miner 

 in the Harz mountains; he studied at Gottingen under Henle and became 

 a district doctor in a provincial town in Posen. In that district there was a 

 serious outbreak of anthrax among the cattle, and the young doctor was 

 thus faced with the problem of this disease. At an early date a French 

 physician, Casimir Joseph Davaine (i8ii-8i), a practitioner in Paris, had 

 discovered small stick-shaped formations in the blood of animals affected 

 with anthrax and through experiments had found them to be producers of 

 the disease, but had not succeeded in ascertaining their course of evolution 

 and method of distribution. Koch took up the problem for fresh treatment; 

 after victoriously struggling against the difficulties that a provincial doctor 

 always experiences when he proposes to carry out experimental research- 

 work, he succeeded in elucidating the entire evolutional history of the 

 anthrax microbe; how, when introduced into the blood of an animal, it prop- 

 agates by repeated division on a vast scale, and then, when the animal has 

 died, these microbes are converted in favourable circumstances into spores 

 possessing great powers of resistance to external influences and the ability, 

 after migrating into a fresh animal host, to start the process of evolution 

 all over again. Koch's genius in these experiments lay in the simple and yet 

 extremely effective technique that he worked out; indeed, it was in this 

 sphere that he afterwards won his greatest successes. The anthrax microbe 

 was at first cultivated in a damp chamber in serum, but Koch soon invented 

 the method of planting bacteria on a gelatin solution; on this substratum, 

 which could be made solid or liquid at will by a slight alteration of tem- 

 perature, it was easy to isolate the bacteria and produce absolutely pure 

 cultures. The method, which in its simplicity is one of the most brilliant 

 inventions of modern times, has been the foundation on which the whole of 

 present-day microbe-research has since then developed. But, in addition to 

 this, Koch introduced the aniline-dye method into the study of bacteria, a 

 method which since that time has been perfected in many ways and one where- 

 by innumerable, otherwise invisible micro-organisms have been discovered 

 and described; and, furthermore, he invented the microscopical illuminating 



