While studying medicine Swammerdam had started to dissect insects and after qualifying as a doctor, Swammerdam focused on insects. His father pressured him to earn a living, but Swammerdam persevered and in late 1669 published "Historia insectorum generalis ofte Algemeene verhandeling van de bloedeloose dierkens" ("The General History of Insects, or General Treatise on little Bloodless Animals"). The treatise summarised his study of insects he had collected in France and around Amsterdam. He countered the prevailing Aristotelian notion that insects were imperfect animals that lacked internal anatomy. Following the publication his father withdrew all financial support. As a result, Swammerdam was forced, at least occasionally, to practice medicine in order to finance his own research. He obtained leave at Amsterdam to dissect the bodies of those who died in the hospital.