Vice-President’s Address. 19 
tissues of the body to the action of the specific poison. In 
the first instance we give this poison in such small doses that 
the protoplasm of the cell, in place of being depressed, is 
stimulated. We try to repeat here what Lister did in the 
case of cilia, stimulating or over-stimulating by a hot wire, 
gradually approached nearer and nearer to the active proto- 
plasm; when some little distance away, the protoplasm was 
stimulated, and the cilia were more active, but when 
approached still nearer the cell protoplasm was over- 
stimulated or depressed, and the movements of the cilia 
became slower, and finally stopped. A strong dose of the 
poison, then, in the same way may depress the cells, but a 
weaker dose may stimulate into greater activity, and so 
enable them to resist a future stronger dose more readily. 
By this method the protoplasm is altered in its resistant 
power so gradually that, ultimately, it may be enabled to 
withstand a very considerable dose of the poison. It is, in fact, 
by a single operation, or more usually by repeated inocula- 
tions of the poison in doses of gradually increasing strength, 
at length able to withstand the action of considerable doses of 
the most virulent poison, of doses as large as can be intro- 
duced under any ordinary circumstances. In this connection, 
however, it must be remembered that no tissues or animals 
can be absolutely protected against the action. of these 
virulent poisons. This is what we should expect. 
As regards this acquired immunity, we have still to learn 
whether it is due to a general increased activity of the cells, 
or to the production of specific powers and products by these 
cells under the modified conditions in which they exist and 
carry on their functions after inoculation. Ingenious argu- 
ments are brought forward on both sides, Metschnikoff 
maintaining that the cells themselves are the main factors in 
the destruction of micro-organisms and their products, whilst 
others, especially those in the German school, maintain that 
the germicidal power rests in the fluids in which the cells 
are bathed, and that the cells can only play the part of 
scavengers in removing dead material. Which of the two 
schools will ultimately triumph—the phagocyte theory school 
or the protective soluble poison school—it is difficult to say. 
