Abstract
Reflex, Definition of. — Originating about the time of Descartes in the seventeenth century, the concept of reflex action grew in time into a most important principle for the interpretation of nervous operations. The founders of the reflex theory and their followers: Descartes (1) and Prokhaska (2), Marshall Hall (3) and Johannes Muller (4), Goltz (5) and Sherrington (6), Magnus (7) and Pulton (8) and many others, regarded reflexes as acts whose ultimate result is determined entirely by the constant properties of the neurons participating in the given reflex and the frequency of the nerve impulses conveyed to the nerve centers from the receptor apparatus. The numerous forms of interaction between various reflexes to be observed in spinal animals, their reciprocal intensification and inhibition, are regarded by the modern reflex theory, or theory of reflexes, as the interaction of nervous elements whose properties are taken as constant. In illustration may I refer to Kato’s (9) hypothesis of the existence of special inhibitory afferent nerve fibers, to Graham Brown's (10) theory of 'half-centers', to Forbes's (11) point of view, to the well-known diagram presented in Sherrington’s (12) monograph illustrating the origin of reciprocal inhibition. The idea that the reflex is a process whose character is determined by constant properties of the elements of a reflex arc Inevitably leads to rejection of all attempts to understand the formation of various reflexes and their development as dependent upon the conditions of the life of a given species or a given individual. The strict definition of a reflex is a "motor response to a sensory stimulus" and it holds true whether or not the higher centers are operating. However, when dealing with reflex responses determined merely by character of the stimulus, strict constancy of reflexes is to be observed in real life only when what is called the ’conscious’ influences of the higher parts of the brain are absent. In view of this, earlier investigations counterposed reflex activity to conscious activity. This is argued most violently by the contemporary Russian school who insist that the activity of the higher parts of the brain are not beyond man's power of knowledge. Those of us who are not materialistic attribute all reflex acts to the activity of the lower parts of the central nervous system, and many prominent investigators of reflex processes have studied reflexes almost exclusively by operative means (experiments on spinal, decapitated and decerebrated animals) or with the aid of narcotics, i.e., eliminated the higher parts of the brain. This procedure totally excludes all possibility of studying reflex acts in the natural conditions of an organism’s life. However, this procedure does not invalidate knowledge of the reflex so obtained. It may be incomplete but not false, so long as the observations are accurate. No one person is expected to solve such problems completely. Due to our intellectual limitations our knowledge of a God-made mechanism must necessarily be fragmentary, especially in the beginning of an investigation. Thus we see that all the normal relations between the organism and its environment were thus left outside the field of experimental scientific investigation of reflex activity.