Before starting upon any given journey, I secured letters from the Department of Fomento, one of the Executive Departments of the Federal Government.

These letters were directed to the governors of the states; they were courteously worded introductions.

From the governors, I received letters of a more vigorous character to the _jefes_ of the districts to be visited.

From the _jefes_, I received stringent orders upon the local governments; these orders entered into no detail, but stated that I had come, recommended by the superior authorities, for scientific investigations; that the local authorities should furnish the necessaries of life at just prices, and that they should supply such help as was necessary for my investigations.

In addition to the orders from the _jefes_ to the town authorities, I carried a general letter from the governor of the state to officials of every grade within its limits.