INTRODUCTORY 11 



by themselves. Some of them have now been successfully 

 cultivated outside the body, notably the microbe of pleuro- 

 pneumonia by Nocard and Roux, and of infantile paralysis by 

 Flexner and Noguchi of New York. 



At the lowest part of the ladder of life, then, there are 

 numerous very simple forms, the animal gradually merging 

 with the vegetable, and to this group of simplest forms the 

 German naturalist, Haeckel, has proposed that the term 

 Protista or Protists should be given. Under this term he 

 includes primitive plants (Protophyta) and primitive animals 

 (Protozoa), both of which will have to be briefly studied under 

 our sub-title of " Man's Microbe Friends and Foes." 



We may now therefore, conveniently review in tabular form 

 the scientific classification of vegetable and animal life, in 

 order to realise the position of these microbe plants and 

 animals, for the fuller consideration of which reference may be 

 made to special works on Botany and Zoology. 



It may be said that these classifications are of interest only 

 to specialists and scientists, but they are included here merely 

 to indicate the orderly arrangement that is necessary in the 

 minuter study of such subjects, and to demonstrate the posi- 

 tion of the group of organisms, whether we call them microbes, 

 germs, bacteria, or designate them by other names. 



It is to the lowest group in each series, the Thallophytes 

 and the Protozoa, that our attention will be more particu- 

 larly directed, and therefore the subdivisions of these special 

 groups are given somewhat more fully. 



CHIEF DIVISIONS OF THE VEGETABLE KINGDOM 



A. Phanerogams or Spermatophyta : these are the time flowering 



plants, and contain the two great groups : 

 I. The Angiospenns : foliacious trees, shrubs, herbaceous plants, 



and grasses. 



II. The Gymnosperms : coniferous or cone-bearing trees (pines, 

 firs, &c.), and their relatives, the cycads. 



B. Cryptogams or non-flowering plants : 



I. Pteridophyta : the ferns, horse-tails, club-mosses, &c. 

 II. Bryophyta : the mosses and liverworts. 



III. Thallophyta: algae, seaweeds, fungi, moulds, bacteria, 

 etc. These are all comparatively simple in structure. 



Classification of the Thallophyta 



This large group is characterised by the absence of any 

 differentiation into root, stem, leaves, etc. Its members are 

 therefore very primitive in structure, and include among their 



