Abstract
The earliest reflex activity elicited by light tactile stimulation in the albino rat has been described. 1 Further investigations have been made upon the fetuses described as non-motile in that contribution. These fetuses do not respond to light tactile stimuli or to the fixative (chemical stimulation). The younger fetuses of this period are also irresponsive to ligation of the umbilical cord (endogenous stimulation). However, the majority of the fetuses of the non-motile stage responded to strong stimulation applied by means of a porcupine quill when stimulated in the neck and fore-limb region. The responses consisted of lateral flexion of the head towards the side stimulated and extension of the fore limbs respectively. Also, some of the older fetuses of this period responded to endogenous stimulation with lateral flexion of the head only. It is evident from these observations that somatic activity, other than that elicited by light tactile stimuli, develops at an earlier period than that described in my previous paper. In addition, these observations show that the younger fetuses responded only to strong mechanical stimuli and the older fetuses responded to both strong mechanical and endogenous stimulation. The responses in respect to these 2 means of stimulation are distinctly different in quality, that is, the contractions elicited by endogenous means are slow, feeble and quickly followed by relaxation; while those elicited by strong mechanical stimuli are also slow and feeble, but maintained. A very long latent period was noticed when strong mechanical stimulation was used.
The fetuses of the early motile stage responded to light tactile stimulation of the snout only, to endogenous stimuli, and to strong mechanical stimulation applied with a porcupine quill. Here again the response differs in relation to the means of stimulation used. The light touch stimulation upon the snout elicited responses of lateral flexion of the head away from the side of stimulation.
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