_Identity of tissue everywhere implies identity of property; and similarity of tissue corresponding similarity of property. Identity of organic connection everywhere implies identity of function; and similarity of organic connection similarity of function._ 87. This law, first formulated by me in 1859, and then applied to the interpretation of nervous functions, was so little understood that for the most part it met with either decided denial or silent neglect; no doubt because of the general disinclination to admit that the properties and functions of the spinal cord could be _similar_ to those of the brain, in correspondence with the similarity of their tissues and organic connections. Even Professor Vulpian, who adopted it, as well as my principal interpretations, hesitated, and relapsed into the orthodox view in assigning three different properties to one and the same tissue in cord, medulla oblongata, and cerebrum.[38] In the course of our inquiries we shall so frequently have to invoke this law that I earnestly beg the reader to meditate upon it, and ask himself upon what other grounds, save those of structure and connection, the properties and functions can possibly rest? If on no other, then similarity in structure and connection by logical necessity involves similarity in property and function. DOES THE FUNCTION DETERMINE THE ORGAN? 88. Closely connected with this law, which simply formulates the self-evident principle that _every action is rigorously determined by the nature of the agent, and the conditions under which the act takes place_, is the surprising question whether functions are dependent upon organs, or organs dependent on functions?--a question which sometimes takes this shape: Is Life the result of organization, or is organization the result of Life?