6 THE ROYAL SOCIETY OF CANADA 
the effects of the growth of bacteria within the tissues has brought to 
light the development of changes in the composition of the blood and 
body fluids, so delicate as to be beyond the range of chemical analysis, 
but so important that upon them depend the continued existence or 
the death of the individual. Properly to employ, for example, the 
methods for the estimation of opsonins, and to administer vaccines in 
accordance with the knowledge so gained, demand the trained specialist. 
The same is true regarding the diagnostic reaction for syphilis afforded 
by the blood serum. The medical bacteriologist here has evolved 
methods of a delicacy far beyond any possessed by the organic chemist. 
They depend, of course, upon chemical changes, but the chemist is in 
this matter lumbering behind. 
Lumbering behind also, I hold, is the non-medical biologist and 
student of heredity. He in his studies upon heredity and variation is 
groping, it seems vainly, for evidence of gross morphological change 
brought about by modifications of environment. He cannot find it, 
and therefore declares that environment must be ‘counted out’ as a 
direct factor in inducing variation. I am filled with wonder and with 
some impatience that he is so blind as to neglect the pregnant data 
afforded by medical investigation into the phenomena of immunity. 
Functional change, obviously, must precede organic or morphological 
change, and if we can prove that, by altering the environment of the body 
cells in particular directions, we can permanently after the functions 
of those body cells, then surely we have established that environment is a 
factor in the production of variation. Now the evidence that this is so, 
obtained by the medical bacteriologist, is overwhelming. Take an 
animal like a rabbit that never in the course of its existence has, or 
whose ancestors so long as rabbits were rabbits can never have been 
exposed to a particular toxin, such as abrin, the active principle of 
Abrus precatorius, the prayer bean, or to a particular microbe such as the 
Cholera spirillum, which for long flourishing in the delta of the Ganges 
only reached Europe and America within the last century. Inoculate 
that rabbit with a small dose of the one or the other, and the animal 
will die. Inoculate it with a still smaller dose and the animal will not 
only recover but what is more its body fluids contain a something, 
absent in the untreated animal, which will neutralise the abrin, or 
destroy the cholera spirilla. In other words, under the influence of un- 
wonted toxins the body cells now alter their functions and discharge 
substances which they had not hitherto produced :—specific substances, 
such that the blood serum of the rabbit immunised against abrin will 
have no effect upon cholera spirilla and that of the rabbit protected 
against cholera spirilla does not render abrin harmless. Nor is this 
a temporary change: it is conveyed to successive cell generations. 
