individuals so constituted that so simple a food as the egg is for
them an active poison.

The lesions produced by the action of injurious conditions are usually
so distinctive in situation and character that by the examination of
the body after death the cause of death can be ascertained. The
lesions of diseases may be very obvious to the naked eye, or in other
cases only the most careful microscopic examination can detect even
the presence of alterations. In the case of poisons the capacity of
the cell for adaptation to unusual conditions is of great importance.
It is probable that certain changes take place within the cells, owing
to which the function can be continued in spite of the unusual
conditions which the presence of the poison brings about. It is in
this way that the habitual use of such poisons as morphine, alcohol
and tobacco, to speak only of those best known, is tolerated. The cell
life can become so accustomed to the presence of poisons that the cell
activities may suffer in their absence.

_Repair_ of the injuries which the body receives is effected in a
variety of ways. We do not know how intracellular repair takes place,
but most probably the cells get rid of the injured areas either by
ejecting them, or chemical changes are produced in the altered cell
substance breaking up and recombining the molecules. When single cells
are destroyed, the loss is made good by new formation of cells, the
cell loss stimulating the formative activity of the cells in the
vicinity. The body maintains a cell and tissue equilibrium, and a loss
is in most cases repaired. The blood fluid lost in a haemorrhage is
quickly restored by a withdrawal of the fluid from the tissues into
the blood, but the cells lost are restored by new formation of cells
in the blood-forming organs. The blood cells are all formed in bone
marrow and in the lymph nodes, and not from the cells which circulate
in the blood, and the stimulus to new cell formation which the loss of
blood brings about affects this remote tissue.

In general, repair takes place most easily in tissues of a simple
character, and where there is the least differentiation of cell
structure for the purposes of function. A high degree of function in
which the cell produces material of a complex character necessitates a
complex chemical apparatus to carry this out, and a complicated
mechanism is formed less easily than a simple one. In certain tissues
the cells have become so