238 POPULAR SCIENCE MONTHLY. 



THE EFFECT OF PHYSICAL AGENTS ON BACTERIAL LIFE.* 



By Dr. ALLAN MACFADYEN, 

 THE JENNER INSTITUTE OF PREVENTIVE MEDICINE. 



THE fact that life did not exist upon the earth at a remote period of 

 time, the possibility of its present existence as well as the pros- 

 pect of its ultimate extinction, can be traced to the operation of certain 

 physical conditions. These physical conditions upon which the main- 

 tenance of life as a whole depends are in their main issues beyond 

 the control of man. We can but study, predict and it may be 

 utilize their effects for our benefit. Life in its individual manifesta- 

 tions is, therefore, conditioned by the physical environment in which 

 it is placed. Life rests on a physical basis, and the main springs of 

 its energies are derived from a larger world outside itself. If these 

 conditions, physical or chemical, are favorable, the functions of life 

 proceed; if unfavorable, they cease — and death ultimately ensues. 

 These factors have been studied and their effects utilized to conserve 

 health or to prevent disease. It is our purpose this evening to study 

 some of the purely physical factors, not in their direct bearing on man, 

 but in relation to much lower forms in the scale of life — forms which 

 constitute in number a family far exceeding that of the human species, 

 and of which we may produce at will in a test-tube, within a few 

 hours, a population equal to that of London. These lowly forms of 

 life — the bacteria — belong to the vegetable kingdom, and each individ- 

 ual is represented by a simple cell. 



These forms of life are ubiquitous in the soil, air and water, and 

 are likewise to be met with in intimate association with plants and 

 animals, whose tissues they may likewise invade with injurious 

 or deadly effects. Their study is commonly termed bacteriology — a 

 term frequently regarded as synonymous with a branch of purely medi- 

 cal investigation. It would be a mistake, however, to suppose that 

 bacteriology is solely concerned with the study of the germs of disease. 

 The dangerous microbes are in a hopeless minority in comparison 

 with the number of those which are continually performing varied 

 and most useful functions in the economy of nature. Their^ wide 

 importance is due to the fact that they insure the resolution and re- 

 distribution of dead and effete organic matter, which if allowed to 

 accumulate would speedily render life impossible on the surface of the 

 earth. If medicine ceased to regard the bacteria, their study would 



* Lecture before the Royal Institution of Great Britain. 



