Vital connections and mechanical connections differ in kind.  You can treat mechanical principles mathematically, but can you treat life mathematically?  Will your formulas and equations apply here?  You can figure out the eclipses of the sun and moon for centuries to come, but who can figure out the eclipses of nations or the overthrow of parties or the failures of great men?  And it is not simply because the problem is so vastly more complex; it is because you are in a world where mathematical principles do not apply.  Mechanical forces will determine the place and shape of every particle of inert matter any number of years or centuries hence, but they will not determine the place and condition of matter imbued with the principle of life.

We can graft living matter, we can even graft a part of one animal’s body into another animal’s body, but the mechanical union which we bring about must be changed into vital union to be a success, the spirit of the body has to second our efforts.  The same in grafting a tree or anything else:  the mechanical union which we effect must become a vital union; and this will not take place without some degree of consanguinity, the live scion must be recognized and adapted by the stock in which we introduce it.

Living matter may be symbolized by a stream; it is ever and never the same; life is a constant becoming; our minds and our bodies are never the same at any two moments of time; life is ceaseless change.

No doubt it is between the stable and the unstable condition of the molecules of matter that life is born.  The static condition to which all things tend is death.  Matter in an unstable condition tends either to explode or to grow or to disintegrate.  So that an explosion bears some analogy to life, only it is quickly over and the static state of the elements is restored.  Life is an infinitely slower explosion, or a prolonged explosion, during which some matter of the organism is being constantly burned up, and thus returned to a state of inorganic repose, while new matter is taken in and kindled and consumed by the fires of life.  One can visualize all this and make it tangible to the intellect.  Get your fire of life started and all is easy, but how to start it is the rub.  Get your explosive compound, and something must break the deadlock of the elements before it will explode.  So in life, what is it that sets up this slow gentle explosion that makes the machinery of our vital economies go—­that draws new matter into the vortex and casts the used-up material out—­in short, that creates and keeps up the unstable condition, the seesaw upon which life depends?  To enable the mind to grasp it we have to invent or posit some principle, call it the vital force, as so many have done and still do, or call it molecular force, as Tyndall does, or the power of God, as our orthodox brethren do, it matters not.  We are on the border-land between the knowable and the unknowable, where the mind can take no further step.  There is no life without carbon and oxygen, hydrogen and nitrogen, but there is a world of these elements without life.  What must be added to them to set up the reaction we call life?  Nothing that chemistry can disclose.