THE METABOLISM OF THE BODY. 473 
trolled by the nervous system in the higher animals, especially 
mammals, and ask, What facts, if any, are opposed to such a 
view? We must suppose that a secretory cell is one that has 
been, in the course of evolution, specialized for this end. What- 
ever may have been the case with protoplasm in its unspecialized 
form, it has been shown that gland-cells can secrete independ- 
ently of blood-supply (pages 321, 416) when the nerves going to 
the gland are stimulated. Now,if these nerves have learned, in 
the course of evolution, to secrete, then in order that they shall 
remain natural (not degenerate) they must of necessity secrete ; 
which means that they must be the subject of a chain of meta- 
bolic processes, of which the final link only is the expulsion of 
formed products. Too much attention was at one time directed 
to the latter. It was forgotten, or rather perhaps unknown, 
that the so-called secretion was only the last of a long series of 
acts of the cell. True, when the cells are left to themselves, 
when no influences reach them from the stimulating nervous 
centers, their metabolism does not at once cease. As we view 
it, they revert to an original ancestral state when they per- 
formed their work, lived their peculiar individual life as less 
specialized forms wholly or partially independent of a nervous 
system. But such divorced cells fail; they do not produce 
normal saliva, their molecular condition goes wrong at once, 
and this is soon followed by departures visible by means of the 
microscope. But just as secretion is usually accompanied by 
excess of blood, so most functional conditions, if not all, de- 
mand an unusual supply of pabulum. This is, however, no 
more a cause of the functional condition than food is a cause 
of aman’s working. It may hamper, if not digested and assimi- 
lated. It becomes, then, apparent that the essential for metab- 
olism is a vital connection with the dominant nervous system. 
It has been objected that the nervous system has a metab- 
olism of its own independent of other regulative influences; 
but in this objection it seems to be forgotten that the nervous 
system is itself made up of parts which are related as higher 
and lower, or at all events which intercommunicate and ener- 
gize one another. We have learned that one muscle-cell has 
power to rouse another to activity when an impulse has reached 
it from a nervous center. Doubtless this phenomenon has 
many parallels in the body, and explains how remotely a nerv- 
ous center may exert its power. It enables one to understand to 
some extent many of those wonderful co-ordinations (obscure 
in detail) that are constantly taking place in the body. We 
