 He complained that preservation was either improperly rendered, ineffectual, or not attempted at all.He also thought that the preservatives used at the time (arsenic-, mercury-, and zinc-based compounds) were injurious to the health of the medical students performing dissections.Later, whilst studying under a phrenologist, he had the opportunity to examine the heads of a number of Egyptian mummies, and concluded that embalming could be achieved without the use of hazardous compounds.