Although much of Johannes Holtfreter’s career was focused on the function of the organizer, first discovered by Hilde Mangold and Hans Spemann, in the early 1940s he turned his attention to the mechanics of gastrulation in amphibian embryos. By closely studying the behaviors of individual cells, he was one of the first to describe how cells collectively give rise the morphogenesis of gastrulating embryos.
Holtfreter’s success in uncovering the cellular behaviors in amphibian embryos was due in large part to his pioneering in vitro culture techniques. To see them more clearly, he explanted single or clumps of cells from different parts of embryos into dishes filled with a balanced salt solution (known today as Holtfreter’s medium) and then examined their movements and changes in shape. When incubated in this medium, the cells could stay alive for weeks.
To observe and document his cultures, Holfreter created numerous beautifully executed drawings. It is clear from his notebooks that his talents as a visual artist played a central role in his research process. Holtfreter took mostly visual notes that often skillfully depicted the three-dimensional structure of the tissue he was looking at. Several of these drawings accompanied the two major papers he published on this study, one in 1943 and the other the following year.