Comparative ontogenetic features of skeletal muscles in physiologically mature and immature mammals.

One series of experiments investigated the time required by such indices of the states of skeletal muscles as membrane potential (MP), action potential (AP), and content of total protein and dense residue to acquire values approximating those found in adults. We established that these indices acquire values approximating those found in adults at the beginning of sexual maturation in both rats and dogs. Chronologically, these values require one-fifth the time to become established in rats as they do in dogs. Another series of experiments investigated the same indices in physiologically mature and immature organisms (rats and dogs). We established that they are much lower in immature than in mature organisms. We conclude that under conditions of natural development the main objects of elimination through natural selection in early developmental periods are physiologically immature organisms.