The present study was undertaken to shed additional light on the somewhat obscure subject of growth of hair. Our test animal was the albino rat, Mus norvegicus-albinus.
The albino rat is born blind and hairless. The eyes open from the fourteenth to the seventeenth day of life, which is about the period of maximum growth of the hair. According to Donaldson,1 the span of life in man is thirty times that of the albino rat. The span of life for the rat is three years; this would be the equivalent of ninety years for man. Figure 1 shows the hairless condition of the rat at birth contrasted with its full growth of hair at the eighteenth day. As far as we have been able to ascertain, this appears to be the most rapid growth of hair in animal life.
During the period of a year we studied the microscopic changes