<prompt> Theory of contagion was first given byParacelsusFracastoriusVesaliusPare  <response>: Fracastorius, an Italian physician enunciated the theory of contagion. He envisaged the transfer of infection minute invisible paicles and explained the cause of epidemics. Ref: 25th edition, Parks Textbook of Preventive and Social Medicine, Page no. 5 