In order to test the vaso-motor reactions of the criminal to various thoughts and emotions, Lombroso made a series of very interesting experiments, during the course of a year, with the sphygmograph and with Mosso’s ingenious and valuable instrument, the plethysmograph. With the sphygmograph (or, rather, the hydrosphygmograph) he observed the degree of excitement produced on various individuals by the sight of wine, cigars, food, money, and photographs of nude women. The plethysmograph is a delicate instrument for measuring mental excitement, depending on the fact that the slightest emotion causes an alteration in the amount of blood present in any part of the body.[53] With the plethysmograph Lombroso found that the strongest impressions (superior to the normal) were produced by cowardice, fear of the judge, some favourite mode of excitement (wine or women), but above all, by vanity. It is not, however, easy to generalise from his observations; it is necessary for such observations to be carried on during a long period on a great number of persons, normal as well as criminal, and to be carefully controlled. They are of very great interest, for they enable us to penetrate into the most secret recesses of the mind, and to measure the force of the motives that move it. It is to be hoped that they will be conducted on a much larger scale than they have hitherto been. All these researches into the physical sensibilities of the criminal are of the first importance, and it is necessary that they should be greatly extended and carefully checked. So far they nearly all converge to show that the criminal is markedly deficient in physical sensibility. On this physical insensibility rests that moral insensibility, or psychical analgesia, as it has been called, which is, as we shall see, the criminal’s most fundamental mental characteristic. CHAPTER IV. CRIMINAL ANTHROPOLOGY (PSYCHICAL). § 1. _Moral Insensibility._