448 Br. Allan Macfadyen [June 8, 



WEEKLY EVENING MEETING, 



Friday, June 8, 1900. 



Sih James Crichton-Browne, M.D. LL.D. F.E.S., Treasurer 

 and Vice-President, in the Chair. 



Allan Macfadyen, M.D. B.Sc, Director of the Jenner Institute of 

 Preventive Medicine. 



The Effect of Physical Agents on Bacterial Life. 



(Abstract.) 



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 prospect 

 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 

 utilise 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 favourable, the functions of life 

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

 These factors have been studied and their effects utilised 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 indivi- 

 dual 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 commouly termed bacteriology — a 

 term frequently regarded as synonymous with a branch of purely 

 medical 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 com- 

 parison 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 ensure the resolution and 



