Sentence:  ... who has more opportunities of acquiring the knowledge, than a physician? He is admitted into the dwellings of all ranks of people, and into the innermost parts of them; he sees them by their fireside, at their tables, and in their beds; he sees them at work, and at their recreations; he sees them in health, in sickness, and in the <WSD>article</WSD> of death; ... 
Meaning of the word marked with <WSD> tags:  A precise point in time; a moment.