Page:Encyclopædia Britannica, Ninth Edition, v. 18.djvu/415

 PATHOLOGY 393 so long as it is clearly understood that the term really explains nothing. There are, indeed, changes described for them in the anterior cornua of the grey matter of the cord, with wasting of the anterior roots of the spinal nerves. &quot;Dissolution &quot; Principle of Nervous Diseases. It is known from &quot; physiological experiment that a muscle is capable of excitation -when the nerve-force is withdrawn from it ; muscular substance is not only a contractile form of protoplasm under the control of nerves, but it has proper irritability when the nervous influence is paralysed (as by the action of the curare poison). The condition of the motor nerves in pseudo-hypertrophic muscular paralysis and in progressive muscular atrophy is such that the muscles are left to their indigenous contractility, being deprived of their innervating force. We shall find these two diseases a convenient opportunity of stating a principle in nervous diseases which has been expounded by Hughlings Jackson under the name of the &quot;dissolution&quot; prin ciple. Morbid states of the nervous system (or many of them) are said to be of the nature of a breaking up of the acquisitions of evolution, with loss of the more finished acquisitions, and a falling back to a simpler type, whose unsuitability to the individual in his then general circumstances amounts to a disease. The illus trations already given ( 4, 5) of &quot;memories&quot; of development inherent in the cellular life of the body belong to the same class of facts or the same order of ideas. In applying this principle to the diseases in question we have to consider both the electrical reaction of the muscles and the retro grade changes in their structure. The reaction of degeneration &quot; is a peculiar one, and it is the diagnostic mark of paralysis of peri pheral origin. The degenerated muscle shows a considerable in crease of irritability for a time imder the galvanic current ; the contraction is sluggish and sustained ; the anodal closure gives a stronger contraction than the kathodal, while, conversely, the kathodal opening has the advantage. These peculiarities of the electrical reaction in &quot; degenerated &quot; muscles are analogous to the physiological reaction when the nerve-influence has been abrogated. We may take it that a &quot;degenerating&quot; muscle falls back upon its proper irritability, that the contractility becomes &quot; ideo-muscular &quot; as contrasted with &quot;neuro-muscular.&quot; The muscle, so to speak, takes lower ground by way of adapting itself to circumstances. In the disease in question, as it alt eets children, the groups of muscles that suffer are precisely those in which the contractility is already of the sluggish, sustained, and ideo-muscular kind, such muscles as the erector spinas, gluta&amp;gt;i, and others, which have an extremely limited nerve -supply in proportion to their bulk. Side by side with this fact we have the other fact of an increase of bulk, as shown in the seemingly strong and hard back, hips, and calves. The paralysis of the muscles has brought with it extreme dilatation of their small arteries, and consequent venous hyperrcmia ; and this presence of the blood in increased quantity has given an enormous impetus to the growth of the interstitial tissue, in the form of young connective tissue and more particularly in the form of fat-tissue. On the other hand, in the muscular atrophy as it affects adults (mostly of the male sex), it is the very nimblest of all the muscles of the body that are picked out first the muscles of the right hand in which the ideo- muscular contractility is naturally small and the neuro-muscular contractility naturally great ; and these muscles, with those of the tongue, undergo a remarkable atrophy with little or no spurious compensation from the interstitial tissue. When the disease pro gresses to other muscles, however, there may be so much new- formed interstitial tissue (fibrous and adipose) that there may be no actual loss of volume in the limb. The precise significance of these differences in the two diseases is not easy to state ; in both the males are very much more often affected than the females, being in the one mostly very young boys beginning to walk, and in the other men whose manual dexterity is a formed habit. The structural changes in the muscular fibre itself are very much the same in both ; as the striation of the fibres disappears the quies cent muscle-nuclei become numerous and prominent. The muscle may be said to fall back upon the more embryonic condition, upon the individual life of the cell-units which had been fused in the fibre ; it retreats to earlier ground, and, as the proper texture of muscle finally goes, the life of the part takes the still more elementary direction of the common binding-tissue and fat. In this sequence of functional and structural events we may discover an illustration of the dissolution principle. The muscles, having lost, or beginning to lose, their innervation, fall back upon the more primitive kind of irritability ; as the downward course of failure proceeds, they retreat still farther to an embryonic structural condition ; when the muscle itself is practically lost the commoner forms of meso- blastic tissue take up the retrograde succession ; and, last stage of all, even the fat and the fibrous tissue waste. 1 ^ See Wilks, Lectures on Diseases of the Nervous System, Lond. , 1878 ; James Ross, Treatise on the Diseases of the Nervous System, 2 vols., 2ded., Lond., 1883; Buzzard, din. Led. on Din. of Nervous Syst., Lond., 1883; Gowers, Epilepsy and other Chronic Convulsive 13. EP.KORS IN THE REGULATION OF THE BODILY HEAT. The constancy of the bodily temperature under all circum stances of external heat and cold of torrid and arctic zones, of summer and winter, of sunshine and darkness is not the least remarkable instance in nature of a self-adapting me chanism. The average internal heat of the human body or of the blood is from 98 to 99 Fahr., and the healthy range in different individuals, or in the same individual at various periods of life, or in various circumstances of exercise and repose, sleeping and waking, is not more than a degree or two below or above the mean. It will be at once apparent that the sensations of heat and cold are no measure of the bodily temperature. The mechanism by which the body s heat is kept uniform is a co-operation of a number of agencies. It is an equation, of which the two sides are the amount of heat produced in the organism and the amount of heat dissipated. In hibernating mammals the former of these is the side to which adaptation is most directed, in such Avise that the whole fires of the animal burn lower while the winter cold lasts. But in man the work and Avaste go on always, and therefore the heat of combustion is practically uniform at all times, so that the adaptation to seasonal and climatic changes of tem perature is mainly on the other side of the equation, the regulation of the amount of heat given off from the body. In cold weather the amount of bodily heat parted with is limited by warm clothing (or clothing which conducts heat with difficulty), by keeping up the temperature of the air artificially by fires, and by the contraction of the surf ace -vessels and other muscular structures in the skin, which has the effect of diminishing the insensible perspiration and makes the familiar sensation of cold. While these adaptations to external cold are decidedly the greatest, it is not to be supposed that there are no adapta tions on the other side of the account. There is, in fact, an increased production of animal heat also, so that more can be parted Avith, and the constant temperature of 98 5 be still unaffected. The increased production is often in the Avay of increased muscular exercise, A 7 hich every one is prone to in cold weather ; it is to some extent also through the more active circulation in all the internal organs, especially brain and liver, their greater functional activity being attended Avith a larger amount of the heat of meta bolic combustion. A heat-forming diet of carbohydrates (chiefly fats), and the physical benefit of the subcutaneous fat resulting therefrom, are Avell-knoAvn elements of the adaptation in colder latitudes. When it comes to be an adaptation to great solar heat, the adaptation is again mostly in the Avay of regulating the heat lost. The vessels of the skin are dilated, and its other muscular elements (in the sweat-glands, &amp;lt;tc.) re laxed (making the familiar sensation of heat), so that per spiration floAvs freely ; the evaporation of the sweat on the surface of the body is constantly consuming heat, and the clothing is Avorn light, and of such colour and texture as will readily conduct heat (both of radiation and of evapora tion). There is noAv as much effort to part with the body s heat as in Avinter there AA as effort to retain it. At the same time the heat of combustion in the body is kept down as much as possible ; muscular exertion is aA T oided, the brain and the digestive functions are less active, and fatty substances are partaken of more sparingly. The various parts of this conservative adaptation are somehoAV co-ordinated through the central nervous system. The vascular system is obviously a chief means by which the body s heat is kept constant, not only by the quick transit of the blood to all parts and the free mixture and Diseases, Loud., 1881, and Morbid Conditions of the Spinal Cord, 3d ed., Lond., 1884 ; J. Hughlings Jackson, &quot;Evolution and Dissolution of the Nervous System,&quot; in Brit. Med. Journ., i., 1884. XVIII. 50