It was in these circumstances that the most fatal infections of typhus took place. Such extraordinary malignancy of typhus happened often when the type of sickness (if indeed there was definite disease at all) among the originally ailing failed to account for it; it was the great disparity of condition that accounted for it. There were, however, more special occasions when a higher degree of malignancy than ordinary was bred or cultivated among the classes at large who were habitually liable to typhus. But even the old pestilential spotted fever which used to precede, accompany, and follow the plague itself, was fatal to a comparatively small proportion of all who had it. Thus, towards the end of the great London plague of 1625, on 18th October, Sir John Coke writes to Lord Brooke: “In London now the tenth person dieth not of those that are sick, and generally the plague seems changed into an ague[176].” One in ten is probably too small a fatality for the old pestilential fever; but that is the usually accepted proportion of deaths to attacks in the typhus fever of later times. The rate of fatality is got, naturally, by striking an average. But in truth an aggregate of typhus cases, however homogeneous in conventional symptoms or type-characters, was not always really homogeneous. We have seen that ninety cases of typhus could occur in the slums of Manchester with only two deaths. On the other hand there were outbreaks of gaol-fever in which half or more of all that were attacked died; and I suspect that the average fatality in typhus of one in ten was often brought up by an admixture of cases of healthy and well-conditioned people who caught a much more malignant type of fever from their contact with those inured to misery. To strike an average is in many instances a convenience and a help to the apprehension of a truth; but for the average to be instructive, the members of the aggregate must be more or less comparable in their circumstances. It has been truly said that there is no common measure between Lazarus and Dives as regards their subjective views of things; it is not a little strange to find that they are just as incommensurable in their risk of dying from the infection of typhus fever. The rule seems to be that the degree of acuteness or violence of an attack of typhus was inversely as the habitual poor condition of the victim. In adducing evidence of the tragic nature of typhus infection conveyed across the gulf of misery to the other side, I shall endeavour to keep strictly to the scientific facts, leaving the moral, if there be a moral (and it is not always obvious), to point itself. Let us take first the common case of country-bred people migrating to the towns. Any lodging in a crowded centre of industry and trade would be high-rented compared with the country cottage which they had left, and they would naturally gravitate to the slums of the city.