90 CLASSIFICATION OF THE BACTERIA. 



by him Bacterium rubescens, and observed that, under varied con- 

 ditions of cultivation, its cells underwent different modifications 

 of form an observation which led him to deny that specific 

 constancy of form existed. He would thereby have anticipated 

 subsequent decisions had the basis on which he relied proved free 

 from objection. This was, however, unfortunately not the case, 

 and, indeed, such a condition was at that time unattainable owing 

 to the lack of irreproachable and reliable methods of cultivation, 

 without which, and the resulting pure cultures, the problem in 

 question cannot be solved. A culture intended for modification 

 experiments may, when examined under the microscope, present 

 a perfectly uniform appearance, and nevertheless contain a few 

 unnoticed individuals of another species, which by their rapid 

 increase when transferred to a medium favourable for their de- 

 velopment may lead to the erroneous supposition that a second 

 and modified form of growth has been produced. By another 

 re-inoculation a third species may be brought into prominence, 

 and so forth. 



A very instructive example of the possibility of similar self- 

 deception is afforded by LISTER'S (I.) striking experiment. He 

 allowed ordinary milk to become sour spontaneously, and then 

 introduced a drop of the liquid into boiled milk, beet-extract, and 

 into urine ; from thence into Pasteur's nutrient solution ; thence 

 into urine again ; and finally back again into milk. Finding, then, 

 that from identical sowings differently shaped cells made their 

 appearance in the various media, he concluded that he had to do 

 with so many changes of form of one and the same organism, 

 Avhich, on account of its origin, he named Bacterium lactis. 



It must not be understood that similar errors were confined to 

 the island of Britain ; on the contrary, they attained their culmi- 

 nation on the Continent in the assumptions of HALLIER (I.) con- 

 cerning the metamorphosis of one fungus into another. It need, 

 therefore, be small matter for surprise that the Austrian surgeon 

 TH. BILLROTH (I.), in a comprehensive work published in 1874, 

 not only attributed all infectious diseases to the agency of a single 

 species of bacterium, susceptible of multiform modifications, but 

 also considered all known bacteria generally as vegetation forms of 

 this one species, viz., Coccobacteria septica. This observer was 

 supported by the botanist NAGELI (VI.), in so far that the latter 

 declared that no necessity existed for the division of the bacteria 

 even into only two specifically different forms. This opinion he 

 still maintained in 1882, notwithstanding the appearance in the 

 interim of a work by Colin containing a number of fresh data 

 calculated to complete and support the theory of difference of 

 species in bacteria. This treatise has already been mentioned in 

 24, because its author upheld the relationship of the fission fungi 

 to fission algae and advocated their collection into one group, 

 Scltizophytes. As at present, however, we are not concerned with 



