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two forms of apoplexy, which are judged based on the familiar symptoms of irregular breathing and pulse. Critical deviations from the natural respiratory rhythm and the corresponding changes in pulse pointed to an incurable form of apoplexy with high likelihood of a fatal outcome. Minor violations of vital functions enabled to make an optimistic prognosis of the course of the disease. However, already at the stage of this distinction, the difference between the views of Galen and the views of the modern doctor with pathogenetic thinking is noticeable. Galen considered breathlessness as only the result of the patient’s failure to move chest muscles. In other words, his ideas are also associated with anatomical-physiological factors, but exist in a different “explanatory model” from today’s—investigative capabilities determine the type of rationality of the scientist.

In order to understand Galen’s views, how he explained the origin of the fit of apoplexy is crucial. To this end, a concrete clinical problem in Galen’s system of general pathology—the theories of the movement of blood and the balance of the four humors—has to be examined. According to the Platonic tradition, of which Galen was an advocate, blood is continuously synthesised from assimilated food. Part of the food, which is useful for this purpose, is absorbed from the stomach and carried through the portal vein to the liver. There, it is converted to venous blood and “vegetative spirit” (pneum, generated by lower part of the soul), which supports the functions of growth and nourishment, and spreads to all parts of the body through veins. Inspired air becomes “vital spirit” (pneum, generated by middle part of the soul) upon entering the left half of the heart. The heart and arteries are responsible for maintaining and distributing natural heat (this was one of the key principles of the medical theory of Aristotle, as interpreted by Galen). This concept explained the fundamental principles of the functioning of the body. Galen believed that, while passing through the arteries, both the blood and the “vital pneuma” warmed up parts of the body, nourished them and maintained their vital function. The transformation of “vital spirit” occurred in the arteries, which formed the so-called “rete mirabile”—a network of vessels which, according to Galen, was located at the base of the brain. It is specifically in the rete mirabile that “vital spirit” turned into the “animal spirit” (pneum, generated by higher part of the soul), which Galen believed was located in brain ventricles (the fourth ventricle played the main role in his theory) and was the mediator for the transmission of motor and sensory pulses to all parts of the body. The transmission process occurred through the flow of the “animal spirit” via nerves, which Galen thought of as hollow tubes. The “animal spirit” reached specific body parts, passing them arbitrary “commands” from the higher, “rational” part of the soul located in the brain. This way, Galen attempted to establish the principles of interaction between the blood circulatory system and the nervous system. His model was based on Plato’s tripartite theory of soul, the concept of the three kinds of pneuma13 and the idea that the brain is the centre of control of the arbitrary functions of the body.

      Galen’s theory was also based on the Hippocratic theory of the four liquids—blood, phlegm, black bile and yellow bile,—and their associated qualities—hot, cold, moist and dry. Overabundance of one of the humors could be the reason for the violation of their good mixture (or “dyscrasia”), leading to the dysfunction of the body in the form of any given disease. Galen considered two scenarios of the development of apoplexy. In one case, he suggested the possible development of apoplexy in the form of local “dyscrasia”; the accumulation of a dense, viscous and sticky fluid in brain ventricles blocked the movement of the “animal spirit”, which in turn made difficult or stopped the transmission of sensory and motor pulses between the brain and other parts of the body. In the other case, which best matched the modern concept of hemorrhagic stroke, apoplexy developed as a result of local plethora. Brain tissue is overfilled with excess blood, which squeezes it. The result of this excess pressure is the impairment of the functions of the brain as the centre of control of body parts. In this case, Galen does not explicitly claim that the plethora of the brain is the result of haemorrhage. Ultimately, at the last stage, both scenarios of the development of the disease lead to a critical change in the temperature of the brain and subsequent cessation of the circulation of the “animal spirit”.

      Galen’s interpretation of the causes of brain injury as the pathological change in the movement of the “animal spirit” enabled to consider disease as a result of anatomical and functional violation of the unity of the spiritual and the corporeal. Furthermore, such a view took into consideration the possible pathogenetic effect of body ageing processes and external factors on the likelihood of the development of apoplexy. During clinical observations, Galen paid attention to the fact that the average body temperature in the elderly was usually lower than in younger people. It followed that their bodies were more susceptible to the so-called cold diseases, for example, caused by excess yellow bile. Also of great significance were climatic and seasonal factors, which influenced the “good mixture” of liquids (for example, sparking an increase in the accumulation of yellow and/or black bile in the body). Overcooling of the brain with subsequent development of bouts of disease could be a result of an unhealthy lifestyle. Any excessive eating was considered harmful: in particular, excessive consumption of wine, according to Galen, reduced natural body heat and was undesirable. The plurality of external factors, such as climate and season, and internal predispositions (age, bad habits, etc) led to the cooling of the body and was the cause of “cold” diseases.

The basic definition of stroke in modern clinical practice is “cerebral circulation disorder”. Of course, the meaning of this nosology changes over time. For instance, in the late 1980s, E.I. Gusev offered the following definition: “Stroke is acute cerebral circulation disorder”.14 Therefore, based on the nature of the pathological process, he divided stroke into ischemic stroke and hemorrhagic stroke. Hemorrhagic strokes are hemorrhages in brain matter and under the brain lining. Mixed forms of stroke were also identified, for example, subarachnoid-parenchymal stroke. Ischemic stroke is basically cerebral infarction as a result of thrombosis or embolism of the extra- or intracranial vessel. The etiological version could be neurothrombotic stroke, which is associated, for example, with atherosclerotic vascular disease. The essence of the matter is the same—violation of blood supply to the brain.15 The interpretation becomes more complicated over time: N. N. Yakhno no longer uses the term “hemorrhagic stroke” in 2007, instead calling this disease “intracerebral hemorrhage”; however, the description of etiology and pathogenesis does not change drastically. “Stroke” now means only what was previously called “ischemic stroke”. This disease certainly belongs to the group of diseases which relate to “acute cerebral circulation disorder”.16 The risk factors for the development of such disorders primarily include arterial hypertension. Furthermore, most authors make reference to old and senile age, hyperlipidemia, hyperglycemia, often associated with insufficient physical activity, obesity and bad habits. It is natural that constant stress and psychoemotional overburden feature among risk factors of stroke itself and among preconditions for the development of its primary cause—arterial hypertension.17 Take note of the fact that the classification of stroke is refined even at the modern-day stage of the development of science: in the twenty years separating the publication of E.I. Gusev’s textbook and the guide edited by N.N. Yakhno, significant amendments18 have been made to this classification.

      Now let us compare Galen’s interpretation of apoplexy and the modern definition of stroke—their similarities and differences are clear straight away. It is interesting that T. Kuhn’s general views on partial incommensurability and the interpretation of the text are brilliantly confirmed by this example. The modern-day meaning of the pathogenesis of stroke is based on the concept of cerebral circulation disorder. This factor basically implies overall disturbance of nutrition and vital activity of the affected part of brain matter. Obviously Galen could not explain the function of the blood, the significance of gas exchange in tissue, etc. However, his understanding of apoplexy

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