These two fundamental principles of the positive system would still be incomplete if they did not come into practical operation according to a general rule, which leads up to the practical organisation of social defence--that is to say, the adaptation of defensive measures to the various criminal types.
The tendency of the classical theories on crime and prison discipline is in sharp contrast, for their ideal is the ``uniformity of punishment'' which lies at the base of all the more recent penal codes.
If for the classical school the criminal is but an average and abstract type, the whole difference of treatment is, of course, reduced to a graduation of the ``amount of crime'' and the ``amount of punishment.'' And then it is natural that this punitive dosing should be more difficult when the punishments are different in kind, and not very similar in their degrees of coincident afflictive and correctional power. Thus the ideal becomes a single punishment, apportioned first by the legislature and then by the judge, in an indefinite number of doses.
Here and there a solitary voice has been heard, even amongst the classical experts, objecting to this tendency towards dogmatic uniformity; but it has had no influence. The question brought forward by M. D'Alinge at the Prison Congress in London (Proceedings, 1872, p. 327), ``whether the moral classification of prisoners ought to be the main foundation of penitentiary systems, either in association or on the cellular plan,'' which he himself decided in the affirmative, was not so much as discussed, and it was not even referred to at the successive Congresses at Stockholm (1878), Rome (1885), and St. Petersburg (1889). On the contrary, the Congress at Stockholm decided that, ``reserving minor and special punishments for certain slight infractions of the law, or for such as do not point to the corrupt nature of their authors, it is desirable to adopt for every prison system the greatest possible legal assimilation of punishments by imprisonment, with no difference except in their duration, and the consequences following upon release.''
 Proceedings, i. 138-70, 551-7, 561-3. Now and then, however, a prison expert of more positive tendencies maintains ``the very great use, or rather the scientific necessity, of the classification of prisoners as a basis for the punitive and prison system'' (Beltrani Scalia.)
To positivists, the ``uniformity of punishment,'' even of mere detention, appears simply absurd, since it ignores the capital fact of different categories of criminals.
There must be homogeneity between the evil and its remedy; for, as Dumesnil says, ``the prisoner is a moral (I would add a physical) patient, more or less curable, and we must apply to him the great principles of the art of medicine. To a diversity of ills we must apply a diversity of remedies.''
In this connection, however, we must avoid the two extremes, uniformity of punishment and the so-called individualisation of punishment, the latter especially in fashion amongst American prison experts. No doubt it would be a desirable thing to apply a particular treatment to each convict, after a physical and psychological study of his individuality, and of the conditions which led him into crime; but this is not practicable when the number of prisoners is very great, and the managing staff have no adequate notions of criminal biology and psychology. How can a governor individualise the penal treatment of four or five hundred prisoners? And does not the cellular system, which reduces the characteristic manifestations of the personal dispositions of prisoners to a minimum, levelling them all by the uniformity of routine and silence, render it impossible to observe and get to know the special character of each condemned person, and so specialising the discipline? Where, too, are we to find the necessary governors and warders who would know how to discharge this difficult duty? The solid fact that particular houses of correction or punishment are in excellent condition when their governors have the psychological intuition of a De Metz, a Crofton, a Spagliardi, or a Roukawichnikoff, and languish when he departs, strikingly demonstrates that the whole secret of success lies in the spirit of a wise governor, skilled in psychology, rather than in the slender virtue of the cell.