I would like to understand what is meant by this expression:
I often asked myself, did the principle of life proceed?
This sentence came in the following context:
When I had arrived at this point and had become as well acquainted with the theory and practice of natural philosophy as depended on the lessons of any of the professors at Ingolstadt, my residence there being no longer conducive to my improvements, I thought of returning to my friends and my native town, when an incident happened that protracted my stay. Whence, I often asked myself, did the principle of life proceed? It was a bold question, and one which has never been considered as a mystery; yet with how many things are we upon the brink of becoming acquainted, if
What is mean by the principle of life here? And how can this principle of life proceed?
There is a meaning underlying in this expression, but I can't understand it.