Xavier Bichat

Marie François Xavier Bichat (/biːˈʃɑː/; French: [biʃa]; 14 November 1771 – 22 July 1802) was a French anatomist and pathologist, known as the father of modern histology. Although he worked without a microscope, Bichat distinguished 21 types of elementary tissues from which the organs of the human body are composed. He was also "the first to propose that tissue is a central element in human anatomy, and he considered organs as collections of often disparate tissues, rather than as entities in themselves". The buccal fat pad (also called Bichat’s fat pad) was named after him.

Although Bichat was "hardly known outside the French medical world" at the time of his early death, forty years later "his system of histology and pathological anatomy had taken both the French and English medical worlds by storm." The Bichatian tissue theory was "largely instrumental in the rise to prominence of hospital doctors" as opposed to empiric therapy, as "diseases were now defined in terms of specific lesions in various tissues, and this lent itself to a classification and a list of diagnoses".