THE IMPERIAL ASPECTS OF CHEMICAL SCIENOE, 
ordinary actions, but has found no need for. providing us with any 
faculty for appreciating without aftificial training the more subtle 
chemical activities which maintain our bodies in life. From the purely 
human point of view our natural disability to understand chemical 
changes introduces a difficulty which has been existent since prehistoric 
times. . 
The progress which has been made in medicine and surgery may 
be quoted as an example of the operation of a chemical factor in the 
occurrences of human life which will seem to most people more subtle 
in its incidence and elucidation than any application of merely mechani- 
cal agencies. In medizval times a man was regarded as aged at fifty; 
the average expectation of life was certainly less than one-half, and 
probably less than one-third, what it is at present. A larger proportion 
of the newly-born of this century survive to the age of seventy than 
attained the age of forty at the period of the English Reformation; 
life in earlier days was a nightmare haunted by apprehension, of 
mysterious pestilences which killed at a few hours’ notice and by minor 
ailments and slight wounds which generally proved fatal: The scien- 
tific use of anesthetics, introduced by Simpson, the scientific application 
of antiseptics, introduced by Lister, and the development of the science 
of preventive medicine, based upon the work of such men as Jenner 
and Pasteur, have changed all this. These new branches of science 
were products of the nineteenth century, and no student can doubt that 
they are still in their early infancy; although they embody scientific 
principles they have in the main progressed to a large extent em- 
pirically. In the near future these branches of human knowledge will 
receive more rigid scientific treatment than they enjoyed in the past, 
and whilst the average expectation of life has been doubled during the 
initiation of the scientific era of medicine, it is safe to premise that 
within another quite short period it will be doubled again. Until a 
few hundred years ago a man was middle-aged at twenty-five, to-day 
he is middle-aged at fifty; within the next fifty years he will attain 
niuddle-age towards one hundred. 4 : ‘ 
Whilst preventive medicine has put into. man’s hands a powerful 
instrument for the alleViation, or, perhaps, rather the postponement, of 
suffering, it cannot be denied that the subject has another aspect. 
During all time previous to the scientific development of preventive 
‘medicine a-natural limit was imposed upon the size of armies; the 
maximum was a few hundred thousands. Every attempt to exceed 
a figure based on such a unit was frustrated by the onslaught 
of a pestilence which speedily reduced the numbers to the normal 
standard recognised alike by Hannibal and Wellington. | Without the 
aid of preventive medicine any army numbering one or two million 
men would, within two months, be reduced by pestilence and disease to 
the pre-scientific standard measured by hundreds of thousands.  Pre- 
ventive medicine has been the enabling cause for the stable existence of 
armies numbered by millions of men, and has been the prime cause 
of the death of innumerable hosts of combatants and non-combatants— 
at a modest computation, fifty millions—by battle, famine, and disease 
over the whole surface of the globe. The potentialities for good in- 
herent in every great branch of scientific progress are invariably reflected 
in potentialities for destruction. ; 
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