Above this fixed point, the symptoms slip and disappear; the index of probability that the clinic provided them with tends to be replaced by a single necessary implication that relates not to temporal frequency but to local constancy: 'Individuals must be regarded as phthisic who are neither feverous, nor thin, nor suffering from purulent expectoration; it is enough that the lungs should he affected by a lesion that tends to disorganize and ulcerate them; phthisis is simply that lesion'.''