I had to confront the issue of heterogeneity. This gamma globulin was really rather weird. When you subjected it to another kind of separation on the basis of its net electric charge, called electrophoresis –another Swedish invention of Arne Tiselius, a person who later became my friend – that molecule sort of developed a smear instead of being a nice sharp peak like albumin in the serum; this thing out of the serum was a smeary peak, and if you cut the peak and put it in you got another peak. And so it looked like it was an enormously heterogeneous molecule, at least in terms of its net electrical charge. Well, that was another problem because you can't... if something is a mixture of a whole bunch of things, you can't do a chemical analysis. The third thing was the specificity, and here I have to come back to the atmosphere of the Rockefeller and how important that was.

Well, I didn't have a mentor; I had a ghost. The ghost was Landsteiner. Landsteiner was perhaps the greatest scientist who ever inhabited the halls of the Rockefeller except perhaps Avery – Oswald Avery who discovered the DNA as the genetic material. And I was fully aware of the ghost of Landsteiner because Landsteiner was the man who allied immunology with organic chemistry; who showed that you could take some organic chemical... little molecule called the hapten by him, and hook it up and stick it into an animal and the animal would make molecules – antibodies – that recognized that hapten and distinguished it in the most remarkable way. An example of the distinction is this, think of a benzene ring, this six-fold structure and put a nitro group in one position and another on another. If you put three nitro groups in symmetrically on that ring it becomes something called picryl – that yellow stuff that's sort of antibacterial – and you could distinguish between dinitrophenyl and trinitrophenyl, just by one nitro group using Landsteiner's methods, which is amazing specificity. And, in fact, what it meant is you could recognize molecules that never existed in the history of the earth before.