In following the processes of digestion, all goes well with his chemistry and his mechanics till he comes to the absorption of food-particles, or their passage through the walls of the intestines into the blood.  Here, the ordinary physical forces fail him, and living matter comes to his aid.  The inner wall of the intestine is not a lifeless membrane, and osmosis will not solve the mystery.  There is something there that seizes hold of the droplets of oil by means of little extruded processes, and then passes them through its own body to excrete them on an inner surface into the blood-vessels.  “This fat absorption thus appears to be a vital process and not one simply controlled by physical forces like osmosis.  Here our explanation runs against what we call ‘vital power’ of the ultimate elements of the body.”  Professor Conn next analyzes the processes of circulation, and his ready-made mechanical concepts carry him along swimmingly, till he tries to explain by them the beating of the heart, and the contraction of the small blood-vessels which regulate the blood-supply.  Here comes in play the mysterious vital power again.  He comes upon the same power when he tries to determine what it is that enables the muscle-fibre to take from the lymph the material needed for its use, and to discard the rest.  The fibre acts as if it knew what it wanted—­a very unmechanical attribute.

Then Professor Conn applies his mechanics and chemistry to the respiratory process and, of course, makes out a very clear case till he comes to the removal of the waste, or ash.  The steam-engine cannot remove its own ash; the “living machine” can.  Much of this ash takes the form of urea, and “the seizing upon the urea by the kidney cells is a vital phenomenon.”  Is not the peristaltic movement of the bowels, by which the solid matter is removed, also a vital phenomenon?  Is not the conception of a pipe or a tube that forces semi-fluid matter along its hollow interior, by the contraction of its walls, quite beyond the reach of mechanics?  The force is as mechanical as the squeezing of the bulb of a syringe by the hand, but in the case of the intestines, what does the squeezing?  The vital force?

When the mechanical and chemical concepts are applied to the phenomena of the nervous system, they work very well till we come to mental phenomena.  When we try to correlate physical energy with thought or consciousness, we are at the end of our tether.  Here is a gulf we cannot span.  The theory of the machine breaks down.  Some other force than material force is demanded here, namely, psychical,—­a force or principle quite beyond the sphere of the analytic method.

Hence Professor Conn concludes that there are vital factors and that they are the primal factors in the organism.  The mechanical and chemical forces are the secondary factors.  It is the primal factors that elude scientific analysis.  Why a muscle contracts, or why a gland secretes, or “why the oxidation of starch in the living machine gives rise to motion, growth, and reproduction, while if the oxidation occurs in the chemist’s laboratory ... it simply gives rise to heat,” are questions he cannot answer.  In all his inquiries into the parts played by mechanical and chemical laws in the organism, he is compelled to “assume as their foundation the simple vital properties of living phenomena.”