N

UMEROUS attempts have been made in the past to discover some tangible method for the purpose of determining the influence of extraneous causes, such as psychic influences, nervous irritants, and especially foodstuffs, on the amylase content of saliva. Without entering into a detailed discussion of the literature on the subject, let it suffice to say that the more recent investigators (and their many co-workers) may be enumerated as follows: A. L. Chittenden, J. P. Pawlow, J. N. Langley, C. L. Evans, L. Michaelis, J. Wohlgemuth, H. P. Pickerill, and others too numerous to mention. By a careful perusal of the enormous mass of literature of the last fifty years, one is primarily impressed with one singular fact,

VOL. LX.-14

i.e. that a number of investigators have approached the subject from a teleologic point of view, and hence have failed to solve the problem. For instance, if we merely feed an experimental subject (and parenthetically it should be emphasized that the subject for the purpose under consideration must be a human being and not an animal, since results drawn from such comparative experiments for numerous reasons are frequently misleading) and examine the amylase content of the saliva during and for some time after the various test meals, only comparative results are obtained which do not portray the actual working conditions of this amylase content.

The fundamental question which a pri

197

TABLE 1.-AVERAGE AMYLOLYTIC INDICES IN 29 PATIENTS SELECTED AT RANDOM.

ori confronts the investigator may be formulated as follows: What working conditions influence the quantity and the action of the amylase content of human saliva? Within limitations, the amylolytic index of human saliva is constantly changing during the various periods of the day. The flow of saliva is solely dependent upon nervous impulses. These These impulses are primarily of a mechanical or chemical nature, although psychic impulses, i.e. fear or the sight of tempting food, have also to be reckoned with; and again, the action of specific drugs, e.g. atropin, pilocarpin, nicotin, markedly affect the salivary secretion. These latter conditions, however, do not play any part in our present consideration. The quantity and to a large extent the quality of secreted saliva are, within certain limits, directly proportional to the intensity of the irritant, primarily foodstuffs, and the mechanism of the masticatory process. Regarding the nervous impulses which control the flow of saliva (or any other glandular secretion) physiologists as yet have not definitely settled which of the two leading theories, that of Heidenhain or that of Langley and Carl son, is the correct one. Heidenhain maintains that with the increase of the ratio of flow the content of salts in the saliva is also increased, the greater the quantity of the secretion the higher being the amount of inorganic constituents. Langley and Carlson, on the other hand, claim that the secretory function of the gland is dependent upon the specific nature of the blood pressure. Accepting the correctness of these two theories for the present, we may assume that any substance entering the oral cavity irritates the endings of centripetal nerves which control the secretion of saliva. Depending upon the quality of the irritant the resultant impulse is conducted to the various parts of the glandular tissue, and thereby causes a flow of saliva of a specific composition. However, it has been demonstrated by Pawlow that if a dog with a gastric fistula is fed a carbohydrate "sham meal," in which food is chewed but not swallowed, no change in the amylase content of the saliva is ob

served while, on the other hand, if the same meal be swallowed, the amylase content proportionally increases. These experiments have been verified by C. L. Evans and in our laboratory. Bayliss and Sterling have furnished a plausible explanation of this most interesting phenomenon. According to these observers, the absorbed foodstuffs act as chemical activators of certain bodies known as hormones, which in turn call forth the secretion of a saliva especially adapted for the respective foodstuffs.

According to carefully conducted experiments by Pawlow and his pupils, the working conditions which govern the flow of saliva may be summarized as follows: The functions of the salivary glands are judiciously adapted to the respective needs, a condition which may be termed "purposiveness." The secretion of saliva occurs only when actually required; it may be caused by the irritation of substances having entered the oral cavity, and to a less extent by the sight of these substances or by psychic impressions. If foodstuffs intended to be swallowed have entered the mouth, a thick, viscid saliva, rich in mucin, is secreted, which lubricates the food bolus and facilitates its ready passage into the stomach. If, on the other hand, substances are brought into the oral cavity which are not intended as foodstuffs but are harmful, a thin, watery secretion is produced which. is calculated to dilute such substances and to aid in expelling them from the mouth. The parotid glands do not secrete saliva rich in mucin, but their product is rich in its content of amylase and other ferments. If acids are brought into the oral cavity the parotid glands quickly pour out a large quantity of saliva rich in alkaline bases and albumin which is designed to dilute the acids. (See Table 2.)

It has also been established that the quantity and the quality of the secretion of all the salivary glands are most markedly influenced by the degree of dryness of the foodstuffs; the dryer the foodstuffs the more rapid the secretion of saliva. The influence of the degree of dryness of the foodstuffs is especially

noticeable in its relation to an increased activity of the parotid glands. There seems to exist a direct interdependence between the rapidity of the flow and the

While the above-noted deductions of Pawlow have been observed in animals with artificially established salivary fistulas, Mitscherlich in 1832, and Za

(After Babkin.)