To abide by the previous examples: 

Firstly, under the head of necessary duty to oneself:  He who contemplates suicide should ask himself whether his action can be consistent with the idea of humanity as an end in itself.  If he destroys himself in order to escape from painful circumstances, he uses a person merely as a mean to maintain a tolerable condition up to the end of life.  But a man is not a thing, that is to say, something which can be used merely as means, but must in all his actions be always considered as an end in himself.  I cannot, therefore, dispose in any way of a man in my own person so as to mutilate him, to damage or kill him. (It belongs to ethics proper to define this principle more precisely so as to avoid all misunderstanding, e. g., as to the amputation of the limbs in order to preserve myself; as to exposing my life to danger with a view to preserve it, &c.  This question is therefore omitted here.)

Secondly, as regards necessary duties, or those of strict obligation, towards others; he who is thinking of making a lying promise to others will see at once that he would be using another man merely as a mean, without the latter containing at the same time the end in himself.  For he whom I propose by such a promise to use for my own purposes cannot possibly assent to my mode of acting towards him, and therefore cannot himself contain the end of this action.  This violation of the principle of humanity in other men is more obvious if we take in examples of attacks on the freedom and property of others.  For then it is clear that he who transgresses the rights of men, intends to use the person of others merely as means, without considering that as rational beings they ought always to be esteemed also as ends, that is, as beings who must be capable of containing in themselves the end of the very same action. [Footnote:  Let it not be thought that the common:  quod tibi non vis fieri, &c., could serve here as the rule or principle.  For it is only a deduction from the former, though with several limitations; it cannot be a universal law, for it does not contain the principle of duties to oneself, nor of the duties of benevolence to others (for many a one would gladly consent that others should not benefit him, provided only that he might be excused from showing benevolence to them), nor finally that of duties of strict obligation to one another, for on this principle the criminal might argue against the judge who punishes him, and so on.]

Thirdly, as regards contingent (meritorious) duties to oneself; it is not enough that the action does not violate humanity in our own person as an end in itself, it must also harmonise with it.  Now there are in humanity capacities of greater perfection which belong to the end that nature has in view in regard to humanity in ourselves as the subject:  to neglect these might perhaps be consistent with the maintenance of humanity as an end in itself, but not with the advancement of this end.