CH. I] THE SCOPE OF THE ENQUIRY 5 



media, in viability, in virulence, in the power to ferment sugars, 

 and so on. ^ 



The environment in which bacteria grow and multiply 

 tends, in the course of time, to "fix" some of these variations 

 by offering to the possessors of them a better chance of survival 

 or perpetuation, so that they ultimately become characteristic 

 of a new species. This is evolution through natural selection. 



By a similar process of artificial selection, as will be shown, 

 we can encourage variation in almost any direction we choose. 

 "Within certain limits the simple forms of life are able to adapt 

 themselves to their surroundings and the adaptation cannot 

 be ascribed to chance for, with a given environment, the one 

 particular alteration in properties surely results." (Adami, 

 1910.) If we so vary the characters of a member of one species 

 that it comes ultimately to possess all the characters of a 

 member of another species, that is "transmutation." The 

 question is, how far can we go in this direction, and to what 

 extent are the recognised species of bacteria I'eally fixed in 

 their characters? 



The Meaning of Species. 



The objection may be raised at this point, that the phrase 

 "transmutation of species" involves a contradiction in terms, 

 since the very definition of "species" excludes the possibility 

 of transmutation. This leads us to a further question, namely, 

 what do we mean by the word "species" as applied to 

 bacteria? — in other words, what determines our present 

 classification ? 



The distinction between different species of bacteria and 

 their recognition depends upon the observation of their charac- 

 ters—morphological, biological, chemical, physiological and 

 pathological. Briefly enumerated these are as follows : — the 

 naked eye appearance of colonies and of a stab culture: 

 microscopic appearances, size, shape, motility, adhesiveness : 

 method of generation and life history, involution forms : power 

 to produce pigment : staining properties : cultural characters, 

 power of growing on different media, in the presence or absence 

 of oxygen, and under different conditions of temperature and 



