Fermentation and Kindred Phenomena. 89 



cases an organism can assume various forms. Zopf, in especial, 

 has maintained the existence of this pleo-morphism, and his 

 system of classification is very much based upon the assumption. 

 In his book he gives drawings taken from actual observations 

 illustrating transformations of this kind. The possibility of 

 these changes occurring adds to the difficulties — already very 

 great — which are experienced in investigating these organisms ; 

 for what means have we of classifying a particular species if it 

 can exist in various forms and be of different sizes ? It is obvious 

 that mere microscopic examination and measurement, which 

 have up to the present time been relied upon in establishing 

 the identity of an organism, completely lose their value. 

 Besides, another set of questions are also raised by this new 

 doctrine, which I may be able to refer to when I come to the 

 consideration of the pathogenic species. 



Having explained, as far as time permits, these few points 

 connected with the life-history of schizomycetes, you will per- 

 mit me to say a few words next relative to the conditions under 

 which they thrive. Their tissues contain much the same pri- 

 mary constituents as are found in ordinary plants and animals 

 — that is to say, the elements Carbon, Hydrogen, Nitrogen, and 

 Oxygen, and in addition certain mineral substances among 

 which are Lime, Potash, Magnesia, and Phosphoric Acid. 



The juices of meat and of vegetables contain the nutriment 

 for these minute organisms in the most readily assimilable form, 

 hence we find them especially suitable for their nourishment, 

 and not only is this the case, but it has also been shown that 

 the various secretions of animals such as blood, saliva, milk, &c, 

 are capable of serving as soils, in which (certain species at least 

 of) organisms thrive well. Some of them, though possibly their 

 number is restricted, can be grown in artificial solutions, such as 

 Pasteur's fluid, but I think it may be stated as a rule that the 

 schizomycetes require for their nourishment more complicated 

 compounds than those which can be prepared in the laboratory. 

 I mean they require albuminoid bodies, of which ordinary 

 white of egg is an example. In this respect they resemble 

 animals and not vegetables, as the latter have the power 



