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 develop- 

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

 converging toward a common type, represented by a large group of 

 unicellular 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. How- 

 ever, even such microorganisms, in which the functions of nutrition, 

 respiration, locomotion, and reproduction are concentrated within 

 the confines of a single cell, and in which adaptation to special con- 

 ditions more readily brings about modifications leading to the pro- 

 duction 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 ten- 

 dency 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 classi- 

 fied with the animals. 



Knowledge of the existence of microorganisms as minute as the 

 ones under discussion was of necessity forced to await the perfec- 

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

 of the seventeenth century, therefore, that the Jesuit, Kircher, in 



