In mid-nineteenth century Germany, the graphic recording of drug effects began simultaneously with the development of pharmacology as an independent science. With the first recording device, the kymograph, drug effects were recorded and compared. A new method for keeping an isolated organ alive facilitated research into the organ's modes of action. Together, these two physiological methods facilitated study of the effects of drugs on organ function. Drug characteristics were discovered and many crude drugs were standardized. Many physiological processes were discovered using these innovative methods. A good example is provided by digitalis, the potency of which varied widely. Digitalis was of great importance in the discovery and treatment of cardiac arrhythmias. Subsequently, many physiological processes were discovered using these innovative approaches to drug research. Pharmacology is a relatively young science, arising from the great progress in chemistry and physiology of the nineteenth century [1, 2]. At the start of the nineteenth century, chemistry made it possible to isolate active substances from medicinal plants, starting with morphine in 1806 [3]. Physiology provided the methodology for pharmacology to become an independent medical discipline. The French physiologist Francois Magendie performed one the first pharmacological experiments with the strychnos tree, from which he isolated the alkaloid strychnine. His successor, Claude Bernard, used active substances, e.g. the Indian arrow poison, curare, as ‘scalpels chimique’ for the ‘dissection’ of physiological processes. In this way he demonstrated that curare acted upon the connection of the nerve with the muscle, the neuromuscular junction [4, 5]. Knowledge from chemistry and physiology together formed the basis for experimental pharmacology. Rudolf Buchheim, the first professor of pharmacology, turned drug discovery from an empirical search for cures into a science [6]. He claimed that the effects of a drug could best be studied by isolating the substance, investigating its chemical composition and correlating the chemistry of the drug with the changes it caused in the function of organs. He also formulated the two main questions for drug research: ‘in which way and to what extent are drugs altered by the body, and in which way and to what extent do they in turn alter the body's function?’ [7]. Such examinations were to be carried out with the same methods as were used in physiology [8]. Oswald Schmiedeberg, Buchheim's most prominent disciple, set up a new laboratory for experimental pharmacology in Strasbourg, then a German city. He was recommended for his post by Carl Ludwig, the great physiologist from Leipzig. Preceding his appointment in Strasbourg, Schmiedeberg had been trained in experimental methodology in Ludwig's institute in Leipzig [9, 10]. Buchheim, Schmiedeberg and Ludwig adapted the research methods of physiology and brought modern pharmacology into being. The two most important physiological methods introduced in early pharmacology were the use of the kymograph and the method of keeping an isolated organ alive. The kymograph was the first device used to document records of experiments, contributing critically to the emergence of pharmacology as an independent science. Pharmacologists adopted the new kymographic methods of conducting physiological experiments for the recording of drug effects, registering changes in physiological function caused by the administration of drugs as a variable in time. This was a great improvement for experimental pharmacology. Carl Ludwig designed the kymograph, or wave writer, in 1847 (Figure 1). Its initial purpose was to improve Poiseuille's manometer, which Ludwig used for the registration of blood pressure in experimental animals [11]. Ludwig was mainly interested in the physiological relation between respiration rate and blood pressure. He measured blood pressure with a mercury-filled manometer attached by a catheter to the artery of an animal. Ludwig experienced difficulties in reading the level of mercury on the manometer accurately, due to the continuous fluctuations. He needed to register the changes of blood pressure and air pressure in the thoracic cavity at exactly the same time. Therefore he put a float on the surface of the mercury and attached a stylus to it. A sheet of smoked paper was placed around the revolving drum of the kymograph. The blood pressure was graphically recorded by the stylus scratching on the paper (Figure 2). In this way the variations in blood pressure were recorded on paper and could be determined exactly. Moreover, the experiment could be reproduced, and the curves could be compared with results from experiments under different conditions. Actually, the kymograph is a universal recording device. Attached to a measuring apparatus, it can record any movement in experimental settings. Figure 1 The Ludwig kymograph and manometer used to record blood pressure (Cyon E. Atlas zur Methodik der Physiologischen Experimente und Vivisectionen. 1876) Figure 2 Curves registered by Carl Ludwig in his experiments on the relation between respiration (thoracic pressure) and blood pressure (Archiv fur Anatomie. Physiologie und wissenschaftliche Medizin. Berlin. 1847) The second contribution of Carl Ludwig was the method of keeping an isolated organ alive by perfusing it in an oxygenated nutrient solution. Ludwig and his co-worker Elias Cyon isolated and cannulated a frog heart, as seen in Figure 3[12]. They used serum obtained from rabbit blood as the perfusion fluid. After the circulation was initiated, the heart started to beat in a very regular rhythm. Ludwig also experimented with an isolated kidney, describing the renal circulation and formulating a filtration–reabsorption hypothesis of urine formation [13]. Figure 3 The isolated perfused frog heart as developed by E. Cyon and Carl Ludwig (Cyon E. Atlas zur Methodik der Physiologischen Experimente und Vivisectionen. 1876) The method of perfusing an isolated heart was improved by Oscar Langendorff for the perfusion of the mammalian heart in 1897 [14]. Langendorff inserted the cannula in the aorta ascendens to effectuate retrograde perfusion. The reverse flow in the aorta closed the aortic valve. In this way, the perfusate flowed through the coronary arteries in order to provide the heart with oxygen and nutrients. Brought together, the kymograph and the isolated perfused frog heart of Carl Ludwig proved to be most useful for experimental research on the effects of drugs on organ function. The drug that was to be studied could easily be added to the perfusion fluid, and the kymograph would record the results. The kymograph was connected to the heart atria and/or ventricles with a string. A lever transferred contractions of the heart to the stylus. The stylus scratched the results on smoked paper on the revolving drum of the kymograph. Because most drugs in Ludwig's time were isolated from plants, any single preparation varied from the others in strength and potency. Assays for determining maximally safe and effective doses had to be developed. The physiological methods of Carl Ludwig were used for these assessments. The first drugs studied in this way were digitalis glycosides.