3. ALTERED SECRETIONS.—Under the influence of disordered innervation secretions may be altered in quantity and in quality. Symptoms of this class may be caused by neural or by central lesions, and the mechanism of their action may be direct or reflex.
(a) After section or lesion by disease of the cervical sympathetic nerve we observe increased activity of the entire skin in the affected area of the head and face: there is more perspiration, lachrymation, and more cerumen is found in the ear. In cases of lesions of a certain part of the oblongata we find one result to be polyuria. In many cases of nerve-injuries the sweat-glands and hair-follicles of the parts supplied by the affected nerve appear to be sometimes abnormally active, or in other cases inactive. In some rare cases of insanity profuse salivation and extraordinary growth of hair are striking symptoms. Lastly, in some functional nervous affections the various secretions and excretions may be altered to extraordinary extremes (e.g. the polyuria and anuria of hysteria).
(b) Qualitative modifications of secretions also occur, as exhibited in the many variations in the composition of the urine in various neuritic conditions, the watery urine of hysteria, the phosphatic urine of neurasthenia. Injuries of a part of the floor of the oblongata (and very probably other lesions of the nervous system) give rise to the appearance of sugar, and sometimes of albumen, in the urine. Under the influence of disease or of an emotion the breast-milk may become toxic to the nursing child, causing diarrhœa, convulsions, etc. In some forms of nervous dyspepsia large quantities of acid or of alkaline fluid may be rapidly poured out into the stomach as a result of disturbed glandular and vaso-motor action. In a few cases of neurosis malodorous or perfumed perspiration has been observed.
In a general way it may be stated that, inasmuch as the normal function of glands is largely, if not exclusively, under direct and reflex nervous control, their secretions may be quickly altered in quantity or quality by rapid nervous disease or by functional disorders. It is probable that much of our future progress in the semeiology of nervous diseases will be in this direction by the aid of improved medical chemistry.
4. ASSIMILATION, METAMORPHOSIS OF FOOD, TISSUE-LIFE, and BLOOD-MAKING are probably under nervous control to a certain extent, but our knowledge is not now in a state to speak positively and definitely of alterations in these processes as symptoms of nervous disease.
THE PRINCIPLES OF DIAGNOSIS.
Having in the preceding pages surveyed the field of neurological semeiology in an analytical way, it remains to briefly indicate how far and in what manner these data can be best utilized for logical diagnosis in the present state of science. If we may be allowed an illustration, we would say that the foregoing sections contain a nearly complete vocabulary of the language of nervous diseases, and that the following pages express an attempt at formulating its grammar.
In the first place, it is important to classify the symptoms observed according to their probable immediate cause in the nervous organs, whether they are due to irritation or to the destruction of parts. The extreme value of such a distinction in practice was first emphatically brought forward by Brown-Séquard in his famous Lectures on the Physiology and Pathology of the Central Nervous System (Philada., 1860); and to the observance of this law of genesis of symptoms we believe that a large part of the subsequent extraordinary progress of neurological science is due.
The symptoms produced by irritation of nervous organs are usually hyperkineses or paræsthesiæ in their various forms. The symptoms, spasm, pain, or numbness, are usually, though by no means always, intermittent. That paralysis and anæsthesia may occur from irritation, by an inhibitory process, is not to be denied, yet we must maintain the extreme rarity of such a mechanism. The phenomena of inhibition are so prominent in the normal nervous system that a physician who looks at nervous diseases from the standpoint of the physiologist may well be excused for seeing morbid inhibitory processes where others do not.