From Suicide pg 120-121:
We must beware, indeed: when one speaks of imitation, one implies a phenomenon of contagion and, not unreasonably, we may pass very easily from the first of these ideas to the other. But is there anything contagious about carrying out a moral precept, or deferring to the authority of tradition or of public opinion? So it is that, just as we think we have reduced two realities to a single entity, what we have in fact done is to confuse two quite distinct notions. In pathological biology, we say that a disease is contagious when it is entirely or almost entirely due to the development of a germ that has introduced itself from outside into the organism. But conversely, to the extent that this germ could only develop thanks to the active cooperation of the environment in which it has settled, the term ‘contagion’ ceases to be appropriate. In the same way, for an action to be attributed to moral contagion, it is not enough for the idea to have been inspired in us by a similar action. It is also necessary that once it has entered the mind, it should automatically and of itself be transformed into movement. In that case, we have a genuine contagion, since it is the external action that, entering us in the form of representation, reproduces itself. There is also imitation, since the new action is everything that it is by virtue of the model that it is copying. But if the impression that the latter creates in us can only produce its effects because of our consent and with our participation, it can then only be called ‘contagion’ figuratively, and the metaphor is inexact, because the determining causes of our action are the reasons that made us consent, and not the example before our eyes. We ourselves are the authors of the action, even though we have not invented it.* Consequently, all those expressions that are so often used, to do with imitative propagation and contagious spread, are not appropriate and should be discarded. They distort the facts instead of describing them and obscure the matter instead of elucidating it.