Slicing and dicing his way through innumerable species, he came to realise that symbiosis between animals and microbes was not a rare phenomenon, as others believed at the time. It was the rule rather than the exception: ‘a widespread, though always supplementary, device, enhancing the vital possibilities of the host animals in a multiplicity of ways’. His decades of work went into a magnum opus called Endosymbiosis of Animals with Plant Microorganisms
