As a rule the saliva presents no deviation from the normal either in quantity or appearance. Occasionally, however, the secretion is considerably increased or is unduly thick and glutinous. A large proportion of the slimy mucus which is vomited in the early morning consists of saliva that has been swallowed during the night. In every case of carcinoma of the stomach there is a great diminution of the sulphocyanide of potassium. During the early stages of the disease the decrease may not be very marked, but as soon as the general nutrition becomes seriously impaired the proportion of the salt steadily diminishes, and it finally disappears altogether. In cases of simple ulcer, on the other hand, the quantity is rarely reduced unless the disease is attended by excessive emaciation.
The production of sulphocyanide of potassium and its elimination in the saliva appear to depend upon three factors, viz. the rapidity of absorption, the integrity of the hepatic cells, and the secretory activity of the salivary glands. Thus, any condition which lessens the absorption of peptones, such as excessive vomiting, atrophy of the stomach and intestine, obstruction of the oesophagus, or deprivation of food, is always accompanied by a diminished elimination of the salt; and the same occurs, though in a lesser degree, in cases of obstruction to the portal circulation. The secretion of sulphocyanide of potassium, like that of urea, is dependent upon the metabolic activity of the hepatic cells. Chronic poisoning by such substances as lead, phosphorus, and arsenic, which retard the functions of the liver, or such diseases as acute yellow atrophy and diffuse cirrhosis, which destroy the tissue of the organ, are always accompanied by a diminution in the quantity of the salt; while excessive salivation from mercury and continued fevers, which lead to functional disorder of the salivary glands, is productive of a similar result.
The main factor in the diminished production of the sulphocyanide in gastric carcinoma seems to be the impairment of digestion and absorption which results from the disease. It is, consequently, most noticeable in cases where the cardiac orifice is obstructed or vomiting is an urgent symptom. As an element in the prognosis we consider the total disappearance of the salt to be of the greatest importance, for we have never known a case to live for more than a month after this phenomenon had been observed. It is important, however, to remember that a patient who presents no sulphocyanide when seen for the first time, will often exhibit a renewed elimination of the salt when he is placed under more favourable conditions and treated by lavage and rectal feeding.
As a rule the quantity of sulphocyanide of potassium present in the saliva may be gauged with sufficient accuracy by comparing the colour produced by the addition of two drops of a solution of perchloride of iron (two drachms to the ounce) to the saliva of the patient with that of a healthy individual. For more accurate work we are in the habit of employing a tintometer the scale of which represents quantities of the sulphocyanide varying from .05 to .7 mgs. The patient is requested to produce as much saliva as possible for two minutes, and to each cubic centimetre of the secretion are added two drops of the solution of ferric perchloride. The mixture is then stirred with a glass rod and filtered through cotton-wool, after which it is compared with the tintometer scale.1