Sentence:  Scarlatina, as an epidemic, does not always assume precisely the same appearance. This diversity depends in part, upon the varying nature and constitution of scarlatina itself, independently of all extrinsic circumstances; in part, upon certain contingencies, which are common to all the inhabitants of a whole district of country, such as the season of the year, the temperature of the air, the <WSD>kindliness</WSD> or inclemency of the weather ... and partly, upon circumstances which apply to individuals, subjected to the disease ... 
Meaning of the word marked with <WSD> tags:  Favourableness; mildness.