Hartline called his father his ‘first and best teacher’ (G&R 1985; Ratliff 1990) and he meant it: Hartline graduated from Bloomsburg State Normal School in 1920, where, as already mentioned, both his parents taught. After Bloomsburg State, Hartline attended a six-week course in comparative anatomy at Cold Spring Harbor Laboratory, in Long Island, NY. In the fall of 1920 he started his studies in biology at Lafayette College in Easton, PA. Most biographies of Hartline mention the influence of Beverly Kunkel, a professor at Lafayette who, among other things, encouraged Hartline to study medicine rather than become a researcher. Hartline’s decision to go to John Hopkins University for his medical degree is partially blamed on Kunkel’s influence. Nevertheless, at Lafayette and under the direction of Kunkel, Hartline made some of his first studies in visual physiology, using land isopods, a diverse order of crustaceans that includes pillbugs and sowbugs.
When he graduated in 1923, Hartline took this work on isopods with him to a summer program at Marine Biological Laboratory, in Woods Hole, MA. This was the first summer of many he would spend at Woods Hole and his personal notes make it clear that the social and scientific community there were one of his main sources of inspiration (G&R 1985, 266). This first summer, Hartline met Jacques Loeb and showed him his work. Loeb was excited enough about the research to have it published in his Journal of General Biology (Hartline 1923). Here Hartline also met Limulus polyphemus (G&R 1985, 267)—the American horseshoe crab.
Limulus is famous in its own right: while members of Limulus’s extended family, the Order Xiphosura (of which only the variety of horseshoe crab are still extant), are so evolutionarily ancient they’re often called “living fossils,” the American Atlantic horseshoe crab is relatively young in evolutionary time—maybe 20 million years old. Limulus is most famous currently for the usefulness of its copper-rich blue blood (Madrigal 2014). A special cell type within this blood, called amoebocytes, makes it invaluable to medical researchers: these amoebocytes have the power to seek out bacteria and trap them inside themselves. Every surgical implant, every injection, every drug certified by the FDA, undergo a test for bacterial contaminates made with Limulus blood called the Limulus amebocyte lysate (LAL). For this reason horseshoe crabs are harvested, bled, and returned to the wild, on industrial scales. Federick Bang, an MBL and John Hopkins scientist, discovered all this about Limulus blood (Bang 1955) thirty years or so after Hartline started poking around in the eye of Limulus. It might be surprising to note that this isn’t Limulus’s only useful contribution to American industry: its body and blood were also used as a soil fertilizer from colonial times basically until the advent of chemical fertilizers.
After his first summer at Woods Hole, Hartline followed advice from his father and his mentor Beverly Kunkel and enrolled at John Hopkins Medical School in Baltimore, MD. He graduated in 1927 stayed for two years as a National Research Council Fellow. All accounts agree that his time in medical school was spent doing as much research as possible and as little medicine as possible, and that he had no real interest in practicing medicine. Hartline spent the rest of his life as an academic researcher studying the biophysics of vision.