It is admitted that a disease may last, and that its various episodes may appear in turn; ever since Hippocrates doctors have calculated the critical days of a disease, and known the significant values of the arterial pulsations: 'When the rebounding pulse appears at each thirtieth pulsation, or thereabouts, the haemorrhage occurs four days later, more or less; when it occurs at every sixteenth pulsation, the haemorrhage will occur in three days' time. .