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We are ignorant Post Date: Sun, 31 Aug 2008 22:43:36 +0000 Although the investigation of these reflexes by physi ologists has been going on now for a long time, it is as yet not nearly finished. Fresh reflexes are continually being discovered. We are ignorant of the properties of those receptor organs for which the effective stimulus arises inside the organism, and the internal reflexes themselves remain a field unexplored. Autor of the post: Undefined Furthermore, the combination and interaction Post Date: Sun, 31 Aug 2008 22:30:55 +0000 The paths by which nervous impulses are conducted in the central nervous system are for the most part little known, or not ascertained at all. The mechanism of inhibitions confined within the central nervous system remains quite obscure: we know something only of those inhibitory reflexes which manifest themselves along the inhibitory efferent nerves. Furthermore, the combination and interaction of different reflexes are as yet insufficiently understood. Autor of the post: Undefined These also take place Post Date: Sun, 31 Aug 2008 22:18:59 +0000 Nevertheless physiologists are succeeding more and more in unravelling the mechanism of these machine-like activities of the organism, and may reasonably be expected to elucidate and control it in the end. To those reflexes which have long been the subject of physiological investigation, and which concern chiefly the activities of separate organs and tissues, there should be added another group of inborn reflexes. These also take place in the nervous system, and they are the inevitable reactions to perfectly definite stimuli. Autor of the post: Undefined Ample evidence was later advanced Post Date: Sun, 31 Aug 2008 22:07:36 +0000 They have to do with reactions of the organism as a whole, and comprise that general behaviour of the animal which has been termed "instinctive 7 Since complete agreement as regards the essential affinity of these reactions to the reflex has not yet been attained, we must discuss this question more fully. We owe to the English philosopher, Herbert Spencer, the suggestion that in stinctive reactions are reflexes. Ample evidence was later advanced by zoologists, physiologists, and students of comparative psychology in support of this. Autor of the post: Undefined To exemplify this we may Post Date: Sun, 31 Aug 2008 21:55:03 +0000 I propose here to bring together the various arguments in favour of this view. Between the simplest reflex and the instinct we can find numerous stages of transition, and among these we are puzzled to find any line of demarcation. To exemplify this we may take the newly hatched chick. Autor of the post: Undefined It has also been maintained Post Date: Sun, 31 Aug 2008 21:43:26 +0000 This little creature reacts by pecking to any stimulus that catches the eye, whether it be a real object or only a stain in the surface it is walking upon. In what way shall we say that this differs from the inclining of the head, the closing of the lids, when something flicks past its eyes? We should call this last a defensive reflex, but the first has been termed a feeding instinct: although in pecking nothing but an inclination of the head and a movement of the beak occurs. It has also been maintained that instincts are more com plex than reflexes. Autor of the post: Undefined It involves also a secretory Post Date: Sun, 31 Aug 2008 21:29:39 +0000 There are, however, exceedingly complex re flexes which nobody would term instincts, We may take vomiting as an example. This is very complex and involves the co-ordination of a large number of muscles (both striped and plain) spread over a large area and usually employed in quite different functions of the organism. It involves also a secretory activity on the part of certain glands which is usually evoked for a quite different purpose. Autor of the post: Undefined A chain of incidents Post Date: Sun, 31 Aug 2008 21:10:26 +0000 Again, it has been assumed that the long train of actions involved in certain instinctive activities affords a distinctive point of contrast with the reflex, which is regarded as always being built on a simple scale. By way of example we may take the building of a nest, or of dwellings in general, by animals. A chain of incidents is linked together: material is gathered and carried to the site chosen; there it is built up and strengthened. Autor of the post: Undefined We are familiar with numerous Post Date: Sun, 31 Aug 2008 20:58:24 +0000 To look upon this as reflex we must assume that one reflex initiates the next follow ing or, in other words, we must regard it as a chain-reflex. But this linking up of activities is not peculiar to instincts alone. We are familiar with numerous reflexes which most certainly fuse into chains. Autor of the post: Undefined Again, we may take Post Date: Sun, 31 Aug 2008 20:38:49 +0000 Thus, for example, if we stimulate an afferent nerve, e. the sciatic nerve, a reflex rise of blood pressure occurs; the high pressure in the left ventricle of the heart, and first part of the aorta, serves as the effective stimulus to a second reflex, this time a depressor reflex which has a moderating influence on the first. Again, we may take one of the chain reflexes recently established by Magnus. 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