How did blood clot in the 18th century?

One of the most curious things about our bodies and medical science today is the way we look at blood. We tend to see its biological facts, based on empirical research, as something universal and timeless. And yet our knowledge is the result of a centuries-long and uncertain endeavour of blood study and experimentation. Our medical ideas about blood has therefore been subject to constant change as well. It has cost medical scientists blood, sweat and tears to gain more insights into this red fluid. It is therefore useful to, every now and then, look back. How did we our predecessors understood blood? What kind of work did they do