Frederick Griffith
  An English bacterioologist by the name of Frederick Griffith was working out a way to identify two strains of Pneumococcus, a bacteria known to cause disease.  Griffith discovered that there were two strains.  One strain produced colonies that had a smooth border, and another that had a rough border.  If he injected mice with the smooth strain, the mice would die of disease.  If he injected mice with the rough strain he found that the mice lived.  Griffith then killed some smooth bacteria under intense heat.  He added the heat killed bacteria to some rough bacteria that were still alive.  He injected this mixture into another group of mice.  Even though the mice were injected with the non-pathogenic rough form of Pneumococcus, the mice still died.  Why did this happen?  The process of transformation was discovered.  The ability of bacteria to "Inherit" traits from another form of bacteria, even though the bacteria were dead.  We now know that bacteria possess a pelleted form of DNA called a plasmid that is transmitted from one bacteria to another upon death of the bacteria.  He knew that something from the smooth bacteria was taken up by the rough bacteria but what it was according to Griffith was still unclear.