78 BACTERIA. 



almost completed his proof of the causal relation of the 

 organism to the disease by the ingenious method of mixing 

 a drop of virulent blood with a large quantity of water, and 

 using the bacteria which fell as sediment as the medium 

 with which to inoculate susceptible animals. With this 

 sediment he was always successful in producing anthrax, 

 whilst inoculation with the water taken from near the 

 surface invariably gave negative results. 



It was not a perfect proof, however, and it was left for 

 Pasteur with his filtration process, and for Koch by his 

 pure cultivation process on solid media, to complete the 

 proof that Davaine so ardently desired and worked to obtain. 



In view of our latter-day knowledge of bacteria, it is 

 interesting to note that as late as 1870, or only twenty years 

 ago, these bacilli of anthrax were declared to be albuminoid 

 crystals ; whilst within the last ten years they have been 

 described as being built up from the d'ebris of fibrinous 

 filaments. 



About this time a great impetus was given to the theory 

 of a living contagion — an impetus which unfortunately im- 

 pelled numerous workers and theorizers to see the cause of 

 disease in every germ that they found. First, Pasteur had 

 formulated his germ theory of fermentation and putrefac- 

 tion ; Davaine, in his descriptive and controversial papers, 

 had insisted upon the connection between his anthrax rods and 

 splenic fever, and in the animal parasitic world the etiological 

 relation between trichina spiralis (a small round worm) and an 

 acute fever, met with especially in pigs, had been fully demon- 

 strated. Salisbury, in this country, thought that he had found 

 the organisms that were the cause of intermittent and remit- 

 tent fevers, of malaria, and of certain other forms of specific 

 disease, but he was quite unable to give proof in any single 

 instance. In Germany, HalUer took up the subject with 

 eagerness. He was led to investigate the subject of Poly- 

 morphism of the bacteria or fission fungi — a theory that had 

 been advanced by Tulasne in 1851, and had been later 

 worked out by Tulasne and De Bary. It was held, indeed, 

 that yeast was simply a form or stage in the develop- 

 ment of certain mould fungi, such as the Penicillia or 

 Aspergilli. 



Pasteur had already pointed out the physiological likeness 

 between the yeasts and the bacteria in their power of pro- 



