The ability of a living organism to receive impressions from the external world and to respond to stimuli is a fundamental characteristic of life. In the context of health and disease, particularly in homeopathy, this inherent capacity to be affected by influences (both pathogenic and therapeutic) is referred to as susceptibility. It is the individual's unique susceptibility that determines how they react to disease agents and to homeopathic medicines.
Let's look at the other options:
\begin{itemize}
\item Enantiopathy refers to a method of treatment by contraries (opposite effects), which is different from the homeopathic principle of "similia similibus curentur" (like cures like).
\item Mongrel sect is not a recognized term in medicine or biology related to the described quality.
\item Venesection is a historical medical procedure involving the incision of a vein for bloodletting.
\end{itemize}
Therefore, the term that accurately describes the general quality of a living organism to receive impressions and react to stimuli is susceptibility.