SECTION I 



THE GENERAL BIOLOGY OF BACTERIA AND THE 

 TECHNIQUE OF BACTERIOLOGICAL STUDY 



CHAPTER I 



THE DEVELOPMENT AND SCOPE OF BACTERIOLOGY 



As we trace back to their ultimate origins the lines of development 

 of living beings of the animal and plant kingdoms, we find them con- 

 verging toward a common type, represented by a large group of uni- 

 cellular organisms, so simple in structure, so unspecialized in function, 

 that their classification in either the realm of plants or that of animals 

 becomes little more than an academic question. However, even such 

 microorganisms, in which the functions of nutrition, respiration, loco- 

 motion, and reproduction are concentrated within the confines of a 

 single cell, and in which adaptation to special conditions more readily 

 brings about modifications leading to the production of a multitude of 

 delicately graded transitional forms, fall into groups which, either in 

 structure or in biological attributes show evidence of a tendency 

 toward one or the other of the great kingdoms. 



Most important of these unicellular forms, for the student of medical 

 science, are the bacteria and the protozoa. 



The former, by reason of their undifferentiated protoplasm, their 

 occasional possession of cellulose membranes, their biological tendency 

 to synthetize, as well as to break down organic compounds, and because 

 of the transitional forms which seem to connect them directly with the 

 lower plants, are generally placed in the plant kingdom. The latter, 

 chiefly on the basis of metabolism, are classified with the animals. 



Knowledge of the existence of microorganisms as minute as the 

 ones under discussion, was of necessity forced to await the perfection of 

 instruments of magnification. It was not until the latter half of the 

 seventeenth century, therefore, that the Jesuit, Kircher, in 1659, and 

 the Dutch linen-draper, van Leeuwenhoek, in 1675, actually saw and 

 3 1 



