From On Suicide pg 215-216. If I understand correctly this is what Durkheim understands by social integration. As he write on pg 216, “to say of a group that it has less communal life than another is also to say that it is less strongly integrated, because the state of integration of a social aggregate merely reflects the intensity of the collective life within it.” In this sense personal particularism sits in tension with social integration because it makes it less likely that collective states will emerge through social interaction.
In reality, what this means is that the density of a group cannot diminish without lessening its vitality. If collective feelings have a particular energy, this is because the force with which each individual consciousness experiences them resounds in all the others and vice versa. So the intensity that they reach depends on the number of consciousnesses that share them. This is why, the greater a crowd is, the more the passions that it unleashes are likely to be violent. Consequently, within a small family, the shared feelings and memories cannot be very intense, because there are not enough consciousnesses to visualize them and reinforce them by sharing. In such a family, it is not possible to form those strong traditions that serve as links between the members of a single group, which even survive them as individuals and join successive generations to one another. Moreover, small families are of necessity ephemeral, and without continuity there can be no unified collectivity. Not only are the collective states within them weak, but they cannot be very numerous, because their number depends on the activity by which views and impressions are exchanged and circulate from one individual to another; and, moreover, this exchange itself is all the faster when there are more people taking part in it. In a sufficiently large community, this circulation is uninterrupted, because there are always social units in contact with one another, while if they are sparse, their relations can only be intermittent and there are moments when communal life is suspended. In the same way, when the family is not extensive, there are never more than a few relatives together, so domestic life is stagnant and there are times when the home is empty.
This was the basis for his account of egotistic suicide. However what he clearly missed is the second-order cultural responses to this emerging situation, making it easier for individuals to cope with being individuals. From pg 224-225:
But society cannot disintegrate without the individual being disengaged from social life to the same extent, without his individual goals taking precedence over those of the community and, in a word, without his personality tending to set itself above the collective personality of the group. The more the groups to which he belongs are weakened, the less he depends on them and the more he consequently comes to depend on himself and recognize no other rules of conduct except those based on his own private interests. So if we agree to describe as egotism this state in which the individual ego affirms itself excessively over the social ego and at the expense of the latter, we might give the name egotistical to the particular type of suicide that results from excessive individualism.
Another way of making this point is to consider the one sidedness of Durkheim’s account of the diffuse currents of anomie which animate an individualised society. There is a great deal here which is plausible but it ignores the possibility that cultural forms might emerge much facilitate coping out of the same mechanism. From pg 230:
This is how currents of depression and disillusion are created that do not arise from any individual in particular but which express the state of disintegration of the society as a whole. What they demonstrate is the loosening of social bonds, a sort of collective asthenia, a social ill, like individual depression, which, when it is chronic, expresses in its own way the poor organic state of the individual. This is when we see the appearance of those metaphysical and religious systems that, by reducing these vague feelings to formulae, set out to prove to mankind that life has no meaning and that one is deceiving oneself by giving it one. This is when new moralities arise which, making a law out of the fact, recommend suicide or, at least, tend in that direction by advising that one should live as short a time as possible. At the moment when these appear, it seems that they have been conjured up from nothing by their creators and the latter are sometimes blamed for the discouragement that they preach. In reality, they are an effect rather than the cause, merely symbolizing the physiological deprivation of the social body in abstract language or in a systematic form.* And since these currents are collective, they derive an authority from that which allows them to impose themselves on the individual and to drive him still more forcibly in the direction towards which he has already been tending as a result of the state of moral disorientation brought about in him by the disintegration of society.