The collective nature of somatic phenomena in the case of great excitement has been much studied, especially among animals, these being simpler and less artificial and therefore easier to understand, and in the long run comparatively like men in the expression of their emotions. Very many animals, according to Darwin, erect their hair or feathers or quills in cases of anxiety, fear, or horror, and nowadays, indeed, involuntarily, in order to exhibit themselves as larger and more terrible. The same rising of the hair even to-day plays a greater role among men than is generally supposed. Everybody has either seen in others or discovered in himself that fear and terror visibly raise the hair. I saw it with especial clearness during an examination when the person under arrest suddenly perceived with clearness, though he was otherwise altogether innocent, in what great danger he stood of being taken for the real criminal. That our hair rises in cases of fear and horror without being visible is shown, I believe, in the well known movement of the hand from forehead to crown. It may be supposed that the hair rises at the roots invisibly but sensibly and thus causes a mild tickling and pricking of the scalp which is reduced by smoothing the head with the hand. This movement, then, is a form of involuntary scratching to remove irritation. That such a characteristic movement is made during examination may therefore be very significant under certain circumstances. Inasmuch as the process is indubitably an influence of the nerves upon the finer and thinner muscle-fibers, it must have a certain resemblance to the process by which, as a consequence of fear, horror, anxiety, or care, the hair more or less suddenly turns white. Such occurrences are in comparatively large numbers historical; G. Pouchet[92] counts up cases in which hair turned white suddenly, (among them one where it happened while the poor sinner was being led to execution). Such cases do not interest us because, even if the accused himself turned grey over night, no evidence is afforded of guilt or innocence. Such an occurrence can be evidential only when the hair changes color demonstrably in the case of a witness. It may then be certainly believed that he had experienced something terrible and aging. But whether he had really experienced this, or merely believed that he had experienced it, can as yet not be discovered, since the belief and the actual event have the same mental and physical result.