882 REPORT—1899. 
be regarded as subdivisions of a class. The point I wish to lay stress on is that 
in any broad classification not more than two tissues are known to be supplied 
with approximate completeness with efferent nerve-fibres. The striated muscular 
tissue, which forms, amongst other parts of the body, the muscles of the limbs and 
trunk, receives in all regions nerve-fibres from the brain or spinal cord. , And the 
unstriated muscular tissue, which forms, amongst other parts of the body, the 
contractile part of the alimentary canal and of the blood-vessels, is in nearly, and 
possibly in all, regions similarly supplied. 
The glandular division of epithelial tissue in some parts responds promptly and 
strikingly to nervous impulses, but in some parts the response is feeble, and in 
others no nervous impulse has been shown to reach the tissue. The connective 
tissue which exists all over the body, and which in its varied forms of connective 
tissue proper—cartilage, bone, teeth, epithelioid cells—makes so considerable part of 
it, is in mammals, so far as we know, destitute of efferent nerve-fibres. The 
epidermic cells, which form a covering for the body, the ciliated cells, the repro- 
ductive cells, do not visibly respond to any nerve stimulus. And the myriads of 
blood corpuscles, which in different ways are in incessant action for the general 
welfare, are naturally out of range of nervous impulses. According to our present 
state of knowledge, large portions of the organism live their own lives uninfluenced, 
except indirectly, by the storms and stresses of the central nervous system. No 
neryous impulse can pass to them to make them contract or to make them secrete, 
or to quicken or slacken their inherent activity. The nervous system can only 
influence them through the medium of some other tissue by changing the quantity 
or quality of the surrounding fluid. 
Regarding, then, the body from the point of view of the control exercised by 
the nervous system on the other constituents, we have first to recognise that this 
control is in considerable part indirect only, that the several tissues are in varying 
degree under direct control, and that different parts of one tissue may be influenced 
by the nervous system to different extents. 
Limitation in the Control of the Nervous System over the different Activities of 
the Cell,—Even when nervous impulses can strikingly affect the vital activity of a 
tissue, their action is limited. They cannot modify the activity in all the various 
ways in which it is modified by the inherent nature of the tissue and the character 
of the surrounding fluid. Thus the submaxillary gland which pours saliva into 
the mouth is in life ceaselessly taking in oxygen and giving out carbonic acid ; it 
does this without pouring forth any secretion. So far as we know no nervous 
impulse can hasten or retard this customary life of the gland by a direct action 
upon it without producing other changes. The nervous system can only do this 
indirectly by modifying the blcod supply The nervous impulse which reaches 
the gland cells causes them to secrete, to take up fluid on one side and to pour it out 
on the other, and it does not, and so far as we know it cannot, confine its influence 
to those changes ordinarily going on in the gland cells. The essential effect of a 
nerve impulse appears to be to modify the amount of energy set free as work; 
usually it causes work to be done, asin the contraction of a muscle, or in the 
secretion of fluid by a gland; sometimes it diminishes the work done, as in the 
cessation of a heart-beat, or the decrease of contraction of a blood-vessel. Other 
changes often go on side by side with this setting free of energy as work, but 
there is no unimpeachable instance in which these other changes take place by 
themselves as the result of nervous excitation. Physiologists have sought for long 
years in all parts of the body for nerves—calorific or frigorific nerves—which 
cause simply an increase or decrease of the heat set free by a tissue ; and for nerves 
—trophic nerves—which cause simply chemical changes in the tissue associated 
with a setting free of heat or not. Probable as the existence of such nerves seems 
to be, the search for them cannot, I think, be said to have been successful. 
Somatic or Voluntary Tissues—When we look at the question of nervous 
control subjectively, and consider in ourselves what tissues are at our beck and 
call, we find that we have immediate and prompt governance over one tissue only, 
the one which, as we have already geen, is most universally supplied with efferent 
nerve-fibres—namoly, the (fibrous) striated muscular tissue, The parts ef the body 
