Nervous diseases are best divided, for the purposes of the consideration of this subject, into organic and functional. In organic disease structural changes are present which are the result of inflammatory change, of vascular disease, or of degenerative conditions, some of which, at least, are toxic in origin. Others are spoken of as degenerative simply; but in some, possibly all, of these there is probably some toxic condition which determines the degenerative change. In a certain class of cases, especially those of the so-called condition of myelitis, it is not easy to discriminate between the different causal factors of the condition, for inflammatory phenomena are present, vascular occlusions are also met with, and degeneration of nervous structures is a constant sequel; and it is not easy to disentangle these different conditions in any given case. It may be said at once that for all such organic diseases no special dietetic rules can be laid down. The usual principles to be observed in the treatment of any acute disease are equally applicable to the acute diseases of the nervous system; for it must be remembered that those diseases are, to a large extent, not diseases of nervous tissue primarily, but really a condition in which disease in other structures leads to the impairment of function of parts of the nervous system. Thus, a case of hemiplegia, the result of occlusion or rupture of a vessel, is really a disease of the vascular system, or of the blood, and the consequent hemiplegia is the result of impaired function of certain nervous structures due to the cutting off of their blood supply. And even later, when actual degenerative changes have taken place in the nervous tissues, these are really of necrotic character, the defective supply of blood leading to the death of the tissues which it supplies. Thus, in malignant endocarditis we may have infarcts in the kidney and in the spleen; we may also have infarcts in the brain, and, as a consequence of that, a condition of hemiplegia. But such a condition is not, strictly speaking, a nervous disease, any more than an infarct of the spleen is a splenic disease, or a fracture of the skull with an injury to the Rolandic region, which causes hemiplegia, a nervous disease. Thus the treatment of the condition of hemiplegia, including the dietetic treatment, is the treatment of.the condition which has given rise to the paralysis: and the treatment of the condition of myelitis, or other inflammatory diseases of the nervous system, is the treatment, so far as diet is concerned, to be observed in the treatment of any acute inflammatory affection of any organ or tissue. If the paralytic condition is the result of such conditions as render care in diet essential, for example, kidney disease, then, of course, the dietetic treatment of the nervous disease, so-called, is determined, or at least modified, by the kidney disease. Similarly the dietetic, and indeed the general treatment of such a condition as embolic hemiplegia in a patient the subject of heart disease is determined, to a large degree at least, by the condition of the heart.
Most degenerative diseases of the nervous system are probably toxic in origin. We know that such a condition as diphtheritic paralysis is definitely so. There are strong reasons for supposing that tabes dorsalis and general paralysis of the insane are a late result of syphilitic intoxication. It would seem, as Gowers has said, as if tabes and general paralysis have a relation to the microbe of syphilis analogous to that which alcoholic peripheral neuritis has to the yeast plant, only that the poison - alcohol - which gives rise to the peripheral neuritis is formed outside the body, whereas the presumed toxine which causes degeneration in the nervous system associated with tabes and general paralysis of the insane, is formed inside the body. Of the disease known as sub-acute combined sclerosis, so often associated with profound anaemia, there is good ground for suspecting that some toxic condition of the blood leads to the very interesting, and not infrequently symmetrical, changes in the spinal cord which are invariably found present in the disease. In pellagra, in which similar spinal cord changes are found, we know the condition to be the result of a poison present in unripe maize. In disseminated sclerosis no poison has yet been isolated, yet the nature of the clinical history of the condition and the conditions found post-mortem lead to the suspicion that the changes in the nervous system are the result of some toxic influence. Such considerations as those are important in reference to the dietetic treatment of the diseases only in so far as they may indicate that good, abundant, and easily-assimilated food must be given in order to maintain the health of the nervous structures, and so enable them to withstand the influence of poisons.
There is a class of nervous disease in which the obvious condition is one of slow, steady wasting or degeneration in certain structures. The cause of this is still obscure. It may be, as has been suggested, that these structures are endowed with a low vitality, and simply die young. If this is so, the condition may truly be called an abiotrophic one. It may be, on the other hand, that some toxic condition underlies this degeneration and determines it. In some cases such a view would seem to be favoured by the clinical history of the cases. In certain instances, for example, of progressive muscular atrophy, after a certain number of muscles have wasted, the result, no doubt, of wasting of the anterior horn cells, which subserve them, the process comes to an end and the disease ceases to be progressive. In such cases - and they are not very uncommon - it would seem as if the supply of the poison had been exhausted, no more being available to affect the still unaffected nerve cells. But even if we suppose that it is a poison which gives rise to those changes, we are still very much in the dark as to its origin. Whether it is a poison generated in the body, or whether it is imported from outside - and in this consideration the question of food will be of the greatest importance - we do not know. In another disease, exactly analagous to progressive muscular atrophy, namely, bulbar paralysis, we are confronted with the same problem. Those diseases are really identical in nature, and are frequently combined. There is another curious disease which Waren Tay first described in which there is a degeneration of the optic nerve and retina, and also a universal degeneration of the motor cells of the nervous system. In this condition, which appears to be invariably fatal, and which occurs in the first two years of life, almost invariably in children of Jewish parentage, we do not yet know whether the condition is one of simple early decay and death - abiotrophy - or whether it may be toxic in origin. Searching inquiries have been made into the feeding and dietary of these children. They have not all been breast-fed, but some have been. So that inquiries into the influence of diet would have to be extended further back than the period of lactation so as to discover any peculiarities in the diet of the mother during her pregnancy. At present we are quite ignorant of the determining cause of this condition, so that no special rules as to diet, with the view of averting or curing the condition, can be laid down.