OF THE

Department of Health of the City of New York

All communications relating to the publications of the Department of Health should be addressed to the Commissioner of Health, 149 Centre St., N. Y.

Entered as second class matter May 7, 1913, at the post office at New York, N. Y., under the Act of August 24, 1912.

Vol. V.

NEW YORK, MAY, 1915.

No. 5

OYSTERS AND CLAMS.*

By Dr. Joseph A. Shears, Sanitary Expert.

My remarks this afternoon will be confined to the subject of oysters and clams. The same facts (with a few exceptions) which apply to oysters apply to clams. The exceptions are as follows:

(1) Clams are capable of locomotion; an oyster is fixed, usually.

(2) The digestion and circulation in a clam is more active and less liable to harbor bacteria for any length of time, consequently clams are less liable to be a source of infection.

This is one of the reasons why clams may be eaten during seasons, and from locations from which the consumption of oysters is dangerous.

(3) Clams prefer a sandy soil; oysters prefer mud.

(4) Soft clams do not hibernate; hard clams and oysters do.

Anatomy and Physiology.

The shell of oysters and clams consists of three layers; outside, a brown horn-like substance; a middle layer of minute prisms of calcium carbonate; and an inner layer called the nacre. The outer and middle layers are secreted from the edge of the mantle of the oyster, and the inner layer from the whole of its outer surface. The lime salts used in the formation of shell material are obtained from the waters in which these shellfish grow, and the thickness of same, and the growth of the oyster, depend upon the amount of lime salts present in the water. It is for this reason we find that the shells vary in size and thickness. The shell is kept closed by the contraction of the adductor muscle; it is opened by the relaxation of this muscle, and the action of a wedged shaped mass of elastic material situated at the inner side of the hinge joint. It is the mechanical action of this elastic material which causes the shell to open when the contraction of the adductor muscle has been interfered with, such as by cutting, or by the death of the oyster. The adductor muscle is commonly known as the heart, and it is the belief among oystermen that when this is cut, it immediately causes death. This belief is untrue, for the oyster may live many hours after this muscle has been destroyed. The heart of the oyster lies just a little above this muscle and its pulsations can be seen when a portion of the pericardium has been removed.

The difference between the right and left shell of an oyster is significant. Most of the near relations of the oyster, like the clam and the fresh water

* A Lecture Delivered Under the Auspices of the Bureau of Public Health Education.

mussel have the two sides of the body, and the two shells alike. These animals are not fastened nor stationary like the oyster; they move from place to place, and their line of locomotion lies in the plane which divides the body into halves; they are erect and bilaterally symmetrical like other locomotile animals. The full grown oyster is not locomotile and lies on its left side, but in the early part of its life it is very active, and is then bilaterally symmetrical like the clam. When it ceases its wanderings and settles down for life, it topples over on its left side, fastens itself by its left shell, which grows deep and spoon shaped, while the right becomes a flat movable lid.

The oyster is equipped with a respiratory, a digestive, a circulatory, a nervous, a reproductive, and an excretory system. It is claimed that oysters have no kidney. Recent researches have found glands to exist which might act as kidneys.

The gills of an oyster form a breathing organ, like the gills of a fish, and keep up a circulation of water within; they also gather up food from the water, and then push it along into the oyster's mouth.

The food of the oyster consists of microscopic organisms, minute animals and plants, which swim in the water. An oyster filters between 8 and 10 gallons of water daily in order to obtain its food. Each microscopic organism is a long time in travelling from the point where it first touches the gill into the oyster's stomach. All this time it is alive, and capable of reproducing its kind, but once within the stomach it is quickly killed. The entire digestive process from the time the food enters the gills of the oyster, until the residue of same is discharged, requires about 18 hours. Of these 18 hours, 13 are required for the food to pass from the gills into the intestinal canal. While most of the organisms serving as food to the oyster are harmless to man, some are extremely dangerous.

The oyster exercises choice in the selection of the organisms comprising its food, rejecting some and swallowing others; among those swallowed are colon bacilli, typhoid bacilli, and others found in sewage, and before these have entered the oyster's stomach, they are favorably placed for chance entrance into the human stomach and, multiplying there, are liable to produce disease.

The color of the oyster depends upon the character of its food and we often find oysters of a green color. The prejudice against green oysters is confined to America; in Europe, such oysters are regarded as superior, and much trouble is taken to impart to them this particular hue. In America, it is difficult to dispose of such oysters. The popular belief is that they are unfit for food or are even poisonous. They often have what is described as a coppery taste, and it is assumed that the green color is due to the presence of copper. To the English and Continental palate this copper taste of an oyster is most desirable and in comparing the American oyster to the European oyster the statement is made: "Nor is anything wanting, save a little of the filings of copper to render them equally relishing, even to an English palate, with the best from Colchester."

Without entering into a prolonged discussion as to the causes operating to bring about these green colorations, and on which points American investigators do not generally agree, it is important to note that all these colorations develop in the autumn, and are caused by pigments accumulating in the blood cells or leucocytes, which in the oyster tend to pass out of the blood vessels and out of the tissues of the gills whenever these are subject to even mild irrita

tion. It is believed that the American oyster is in a debilitated condition, or, at least, in a condition of reduced vital activity at the time the green coloration develops.

As the result of investigations, it can be stated that the hypothesis that green oysters are in a debilitated condition cannot be entirely true, for the green coloration occurs frequently in oysters in America when they are in the finest physical condition. In fact, this is almost the rule rather than the exception. But it can also be stated that all the available evidence tends to show that oysters in which green coloration has recently taken place are not physiologically active.

Greenness, according to some investigators, consists in a more or less abortive effort on the part of the oyster to disgorge certain excretionory materials with a consequent accumulation of them in the blood cells near the surface of the oyster's body. This occurs as the result of overfeeding on certain types of foods, followed by a period of inactivity. Such conditions develop most commonly in the autumn, hence the most frequent occurrence of green oysters at that time. The color may be removed from the oyster by transferring it for a short time to water in which the green food is deficient. Greening is not a disease nor produced by a parasite or a poisonous material in any sense.

Reproduction.

American oysters are either male or female. European oysters (French and English) are bi-sexual. The sex of a European oyster often varies in the same subject. A male oyster, for example, will change into half male, half female, and then into a female. It is claimed that the female oyster is the superior sex. The male is weaker and inferior in every way, and, when badly nourished, a female oyster will degenerate into a male. Like other mollusks, the oyster reproduces by eggs; each egg laying oyster produces more than 1,000,000 ova in a single season. When the reproductive elements are fully ripe, they are thrown out into the water to be fertilized by accident, and while many of them meet with male cells, innumerable multitudes sink to the bottom and are lost. It is fortunate that this is the case for our oyster is so prolific that if all the eggs were to be fertilized, and were to live to grow to maturity, they would fill up the entire bay in a single season. An unusually large American oyster will yield nearly 1 cubic inch of eggs, which in number would be about 60,000,000.

For a brief period after hatching, the free swimming larvae are carried about in the water by tides and currents for long distances. Many never mature, as they are destroyed by cold and living enemies. When about two weeks old, the young or, as they are commonly called, spat oysters, have secreted shells of sufficient weight to cause them to gravitate to the bottom of the beds, and here they attach to any object with which they come in contact. At the end of one season the spat has grown to about one inch in diameter. season the oyster is ready for the process of reproduction.

"Floating."

At about the third

Floating of oysters for the market is a common practice in this vicinity., Osyters are placed in partly submerged floats or rafts in water containing less salt than that over the oyster beds. The oysters are left on these floats, usually

during the time of two to four changes of tide. Oysters so placed, open the mouth of their shells, after lying quiet for a longer or shorter period, and then breathe or drink (draw in) the water, as they do when feeding on their original beds. Hence the process is called "giving the oysters a drink," also "freshening."

The reason for this practice is manifold:

(1) The oysters clean the mud and sand out that was in them when taken from the beds.

(2) The flesh of the oyster swells so as to occupy nearly one-fifth more volume.

(3) The flesh becomes whiter and firmer.

(4) Such oysters do not shrink so much or so rapidly after being shucked from the shell.

This "fattening" process consists simply in the absorption by the oyster of water. This absorption takes place through the attraction between the fresh water and the mineral salts in solution in the tissues of the oysters. Swelling or "fattening" can only take place when oysters are placed in water of less salt content than that in which they have been for a considerable time. No additional nutrient substance is incorporated by this process; the practice constitutes an adulteration and a deception.

As floating is often done in creeks that bring down fresh water drainage from the land, and as such creeks are liable to sewage contamination, floating introduces a real menace to health. One of the great dangers arising from the practice is the fact that as oysters are often consumed raw, they become active factors in the propagation of disease.

Typhoid and the Oyster.

That the practice of fattening oysters in the mouths of rivers in the vicinity of sewers is dangerous to the public health is beyond question and is shown by the combination of conditions which have made it possible to trace typhoid outbreaks to the eating of a lot of raw oysters. It is most fortunate that the typhoid organism is not a hardy one; it probably lives but a short time under the unfavorable conditions found in sea water. Those that do survive are diluted in the enormous amount of water, ebbing and flowing with the tide, that few, if any, of them reach the oyster beds, and those that do reach the oysters, are digested and destroyed by the feeding apparatus of the oyster. There is no evidence that oysters taken directly from their growing beds, even though these beds be polluted to a certain extent, have ever caused disease. It is very different with floated oysters; here we find instances where oysters have been placed directly at the mouths of typhoid-ladened sewers or creeks, for hours just previous to sale. No better scheme for the direct infection of such shellfish could be found, unless the germs were inserted directly between the shells. In investigating the epidemiology of typhoid from oysters, it was found:

First: That the discovered outbreaks of typhoid fever due to the eating of raw oysters, or other shellfish, have been few in number.

Second: That the existence of so-called endemic typhoid conditions, as distinguished from outbreaks, is considered to be a matter requiring more definite proof in each instance than has heretofore been brought forth.