- Emil Reymond (1818-1896) | Age: 24
- Ernst Brucke (1819-1892) | Age: 23
- Carl Ludwig (1816-1895) | Age: 26
- Hermann Helmholtz (1821-1894) | Age: 21
In opposition to views of their anatomy and physiology professor:
- Johannes Muller (1801-1858) | Age: 41
who held the view, in lecture, and in print, e.g. his Manual of Human Physiology, that there appears to be "something in the phenomena of living beings which cannot be explained by ordinary mechanical, physical or chemical laws".
In 1833, Johannes Muller, in his Manual of Human Physiology, penned while chair of anatomy and physiology at University of Berlin, systematically summed up all the dogmatic vitalism of history, surpassing his predecessors in essentials, yielding a wide influence. Here, he was promoting the following views:
- “Though there appears to be something in the phenomena of living beings which cannot be explained by ordinary mechanical, physical or chemical laws, much may be so explained, and we may without fear push these explanations as far as we can, so long as we keep to the solid ground of observation and experiment.”
- — Johannes Muller (1833), Elements of Human Physiology (pg. #).
Muller, in his new physiology, rejected the romantic spirit of the old physiology, but kept or embraced vitalism, being convinced that there were differences between organic and inorganic, and would not accept physical laws as determining factors in physiologic processes.
In 1840, Muller, in his second volume, began to touch on mental phenomena:
- “The ‘will’ sets in activity the nervous fibers like the keys of a piano.”
- — Johannes Muller (1840), Elements of Human Physiology, Volume Two (pg. #) 
Muller argued, throughout these publications, that there is "something else", other than "selective affinity" (chemical force), which rules in life. Muller, moreover, later expressed the view, which he told to Richard Owen (who told this to Darwin), that life had a special "organizing energy" that controlled evolution.
In 1834, Carl Ludwig, at the University of Marburg, began working towards is medical degree, but got expelled at the end of the winter semester 1835/36 because he campaigned for a politically persecuted student. In 1839, Ludwig completed his doctorate at Margug. Then, in 1842, he completed his habilitation in Marburg with his work "Contributions to the doctrine of the mechanism of urinary secretion", wherein he opposed the notion of vis vitalis, still prevalent at the time, and postulated that urine primarily arises as a filtrate of the glomeruli via the driving force of blood pressure and that it receives its final composition through resorption processes along the renal tubules.
In 1838, Emil Reymond, aged 20, read Lucretius’ On the Nature of Things, which converted him to a positivist view of biology, wherein he dispensed with teleology, vitalism, and other romantic notions.
In 1838, Ernest Brucke studied medicine at the University of Berlin, then the University of Heidelberg, then and again in Berlin, where he received his doctorate in 1842 under Johannes Muller, with a thesis on diffusion processes. In 1843, Brucke became Muller's assistant, and he achieved his habilitation in 1844 (Privatdozentur) and from 1846 he taught anatomy at the Academy of Fine Arts in Berlin.
In 1841, Hermann Helmholtz, enticed by Muller's motto of "creation of new phenomena through experimentation", decided to write his dissertation under Muller's supervision, specifically on the microscopic examination of the nervous system.
During this period, a close friendship formed between Reymond, Brucke, Helmholtz, and Ludwig.
In 1842, Reymond, aged 24, wrote to Carl Ludwig, aged 26, that he and Ernst Brucke, aged 23, had “pledged a solemn oath to put into effect” their unified belief that there are no vital forces in nature, but only physical or chemical forces. The following is the oath:
- “We pledge to put in power this truth: NO ‘other’ forces than the common physical chemical ones are active within the organism. In those cases which cannot at the time be explained by these forces one has either to find a specific way or form of their action by means of physical mathematical method, or to assume new forces equal in dignity to the chemical-physical forces inherent in matter, reducible to the force of attraction and repulsion.”
- — Emil Reymond (1842), “Physical Chemical Force Oath” (co-author: Ernst Brucke)
Later, by 1845 or 1847, Carl Ludwig and Hermann Helmholtz, also signed the oath.
Signed in blood
In 1967, Paul Lee, in California, during his meeting of Alan Chadwick, amid the the rise of the “organic movement” of gardening, spoke of the Reymond Brucke blood oath as follows:
- “I gave Rodale and Berry my talk on the physicalist/vitalist conflict, and where Rodale's father came in, much like I did for the students and faculty at Emerson College, on Steiner, some years later, and his place within the physicalist/vitalist conflict. I told them about 1828 and the smoking gun—the artificial synthesis of urea—and the presumed refutation and defeat of vitalism and the victory of physicalism. I told them how this chemical blow had subverted the term organic to mean ‘artificial synthesis’, the aim of organic chemistry, and how this blow added to that other blow of some hundreds of years before, when Galileo mathematized nature, the blow of mathematical physics, the beginning of the reduction of organic nature to matter. Physicalism was the name for the ideological takeover of what counted for knowledge, the inner core of the scientific revolution and the content of the new paradigm. I told them about the Physicalist Society in Berlin and the oath taken in blood to drive out any closet vitalists, as they closed ranks behind Helmholtz and Muller and DuBois-Reymond and Brucke. Then came the mopping up operation of the logical positivists in Vienna and the circle around Carnap and Neurath and their theme of the ‘elimination of metaphysics’ and anything suggestive of vitalist sympathies, and how religious language, ethical language, and aesthetic language was regarded as nonsense, strictly nonsense, literally nonsense. No wonder old man Rodale had to recover and reaffirm the integrity of organic nature against the takeover of industrial society and reductive, physicalistic scientism.”
- — Paul Lee (1967), “On Meeting Alan Chadwick and the Organic Movement”, in: There is a Garden in the Mind (pg. 140) 
As to when or who exactly signed the oath in blood, the details are a bit wanting? One reference states that it was just Reymond, Brucke, and Ludwig, and that it was on "sealed in blood" (Greenwood, 2015). Generally, the blood signing part it is categorized as an "as legend has it" (Wertheimer, 2012) type of origin. Presumably, there is some truth to the legend.
German Physical Society
In 1845 Brucke and Reymond, together with four other young physicists, including the physicist Heinrich Magnus, founded the German Physical Society (Deutsche Physikalische Gesellschaft), using their oath as the credo of the new society.
The oath pact that would form the basis of the new “physicalist physiology” of the future.
In respect to terminology reform, and what exactly Reymond and Brucke were objecting to, we can glean a certain amount of Greek and German, and later translation to English confusions. The following is one example:
- “They were, all of them, Shelley, Byron, Mary Shelley, and Victor Frankenstein, obsessed with the recent findings of Galvani, Volta and Aldini, and by the notion that electricity is the secret essence of life. And I will go further, and suggest that Reymond had the same obsession. Reymond, the great opponent of vitalism, had scorned the idea of a lebenskraft or life force. And yet he had proposed to relate the electrical characteristics of nerve and muscle to their ‘general vital activity’. And he spoke of the impact of Galvani's work of 1791 as being almost equal to the impact of the French Revolution.”
- — Paul Cranefield (1988), “Carl Ludwig and Emil du Bois-Reymond” (pg. 278)
Here, Reymond objects to "life force" (lebenskraft), while at the same time employing the term "vital activity"? In other words, he rejects life forces operating in organisms but accepts not vitalism, per se, but "general vital activity". Prolonged digression along this path, is what leads to abioism, wherein the closet get cleaned.
In 1848, Reymond, in his Studies on Animal Electricity, which illustrates a horse falling into a pond filled with electric eels, was applying the oath as follows:
- “I cherish the firm conviction that the physico-mathematical research method correctly applied, is in a position to do a great service to organic physics.”
- — Emile Reymond (1848), Studies on Animal Electricity
Reymond, in his "organic physics" term, seems to be digging at the physics of organisms? This logic began to meet the start of its new terminology reformulation in Alfred Lotka's Elements of Physical Biology (1925), wherein the first chapter was "Regarding Definitions".
Brucke, of note, later, at Vienna University, became the medical school advisor to Sigmund Freud, who adopted this oath.
- (a) Muller, Johannes. (1833). Elements of Human Physiology, Volume One. Publisher.
(b) Muller, Johannes. (1840). Elements of Human Physiology, Volume Two. Publisher, 1844.
(c) Driesch, Hans. (1914). The History and Theory of Vitalism (translator: Charles Ogden) (§: Johannes Muller, pgs. 113-). Publisher.
- Zimmer, Heinz-Gerd. (2006). “Johannes Muller” (pdf), Clinical Cardiology, 29:327-28.
- Humes, Edwards. (2007). Monkey Girl: Evolution, Education, Religion, and the Battle for America’s Soul (pg. 115). Harper Perennial.
- Carl Ludwig (German → English) – Wikipedia.
- Finkelstein, Gabriel. (2015). “Scientific Celebrity: the Paradoxical Case of Emil du Bois-Reymond” (Ѻ), talk delivered at the Annual Meeting of the History of Science Society, Nov 20.
- Emile Reymond – Britannica 1911.
- Cahan, David (1993). Hermann von Helmholtz and the Foundations of Nineteenth-Century Science (pg. 24). University of California Press.
- Lee, Paul. (2013). There is a Garden in the Mind: a Memoir of Alan Chadwick and the Organic Movement in California (oath, pgs. 85, 140). North Atlantic Book.
- Greenwood, John. (2015). A Conceptual History of Psychology (pgs. 170-71). Cambridge.
- Wertheimer, Michael. (2012). A Brief History of Psychology (pg. 63). Taylor & Francis.
- Porter, Alan. (2020). Knowledge in a Nutshell: Sigmund Freud: The complete guide to the great psychologist, including dreams, hypnosis and psychoanalysis (pg. #). Publisher.
- Author. (1964). “Article” (letter, pg. 10; oath, pgs, 10, 35, 47, 192), Psychological Issues, Volume Four. University Press.
- Dyer, Ray. (2021). “Freud and the Helmholtz School” (Ѻ), Victorian Web, Feb 11.
- Cranefield, Paul. (1988), “Carl Ludwig and Emil du Bois-Reymond: a Study in Contrasts” (pg. 278), Gesnerus, 45:271-82.
- Reymond, Emile. (1848). Studies on Animal Electricity (Untersuchungen uber thierische Elektricitat). Berlin.
- Cranefield, Paul F. (1957). “The Organic Physics of 1847 and the Biophysics of Today” (JST), Journal of the History of Medicine and Allied Sciences, 12(4):407-23, Oct.
- Reymond-Brucke oath – Hmolpedia 2020.