Linus Pauling: The red protein in the blood, hemoglobin, has interested me for a long time, has
a beautiful color. When I was a young graduate student beginning, I saw in the chemical
library at the California Institute of Technology, some big green volumes which I
looked at through curiosity. They were by, I'm not quite sure, Brown and Schuckert
or something like that. These investigators had collected blood from a lot of different
animals. They separated the red corpuscles and hemolyzed them and let the hemoglobin
crystallize and then took photographs of these hemoglobin crystals. And the crystals
all looked different, from one animal species to another animal species. Each animal
species manufactures its own kind. Human beings manufacture human hemoglobin, fetal
humans manufacture fetal hemoglobin, which is more like fetal calf hemoglobin, say,
than adult human hemoglobin -- the fetuses of the world are more closely related to
one another in some way than they are to the adults of their own species. And of
course, now we know that about three-hundred different kinds of human hemoglobins
are manufactured by adult human beings. So that's another example of biological specificity.
