After earning his medical doctorate in 1872, he worked briefly as a hospital assistant at the Berlin Charité.
His clinic was known for being technologically advanced, and it was the first to have a Finsen ultraviolet light therapy device and X-ray machine.
Lassar is remembered for the creation of public bath houses for low-income individuals in Germany and Austria.
"[1] He was very social, and he invited physicians who made referrals to his clinic to a champagne breakfast twice a year.
[2] In addition, Lassar was the first to assemble a collection of moulage (model injuries for training purposes) in Germany.