[1620] and yet the lord so upheld these persons, as in this general calamity they were not at all infected either with sickness, or lameness. and what i have said of these, i may say of many others who died . . that whilst they had health, yea, or any strength continuing, they were not wanting to any that had need of them. based on the above passage, to what did bradford attribute the fact that some people survived the disease in plymouth?