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haps be permissible to cite a few of the statistics. I give more details than would perhaps be appropriate in these pages, were it not for the novelty of the results, and the importance of their bearing upon the physiology of absorption of nutritive material in our bodies as well as upon the nutritive value of the oysters.
The changes in the constituents of the body (“flesh") were mainly such as would be caused by osmose, though there were indications of secretion of nitrogenous matters and, especially, of fats, which are not so easily explained by osmose. This I will speak of later.
The amounts of gain and loss of constituents which the bodies of the oysters experienced may be estimated either by comparing the percentages found by analysis before and after dialysis, or by comparing the absolute weight of a given quantity of flesh and the weights of each of its ingredients before, with the weights of the same flesh and of its ingredients after, dialysis. For the estimate by the first method we have simply to compare the results of the analyses of the floated and the not-floated specimens. Taking the averages of the two experiments, it appears thatThe percentages of
After dialysis Water rose from ...
82:4 Water-free substance fell from
17.6 Total flesh....
100.0 Protein fell from..
8.9 Fat fell from ...
1.9 Carbohydrates, etc., fell from
6.2 Mineral salts fell from
1.6 Total water-free substance in flesh
17.6 There was, accordingly, a gain in the percentage of water and a loss in that of each of the ingredients of the water-free substance. This accords exactly with the supposition that during the floating the flesh gained water and lost salts and other ingredients.
It will be more to the point to note the absolute increase and decrease in amounts of flesh and its constituents—in other words, the absolute gain or loss of each in the floating. Estimates by this method have been made and explained in the detailed accounts referred to. They make it appear that 100 grammes of the flesh as it came from the salt water was increased by floating, in one specimen, to 120.9, and in the other to 113.4 grammes. This is equivalent to saying that the two specimens of flesh gained in the floating, respectively, 20.9 and 134 per cent, or, on the average, 17.3 per cent of their original weight. By the same estimates the water-free substance in the 100 grammes of flesh before the floating weighed, on the average, 22.1 grammes, while that of the same flesh after floating weighed only 20.6 grammes, making a loss of 1.5 gramme or 6:6 per cent of the 22•1 grammes which the water-free substance weighed before dialysis. The main
results of the two experiments thus computed, may be stated as
Before dialysis. After dialysis.
77.9 grammes to 96-6 grammes. Water-free substance fell from
20-6 Whole flesh rose from ....
100.0 Protein was assumed to remain the same. 10.5
10:55 Fats fell from ...
2.3 Carbohydrates, etc., fell from
6.0 Mineral salts fell from .
In brief, according to these computations, the flesh lost between one sixth and one seventh of its mineral salts, one eighth of its carbohydrates, and one twelfth of its fats, but gained enough water to make up this loss and to increase its whole weight by an amount equal to from one seventh to one fifth of the original weight. Assuming the loss of nutritive value to be measured by the carbohydrates and fats which escaped, it would amount to about one tenth of the whole. That is to say, the total nutritive materials were one tenth less after floating than before.
In the liquid portion of the shell-contents, the percentage of water rose and that of the water-free substance fell in a very marked degree. But while the whole percentage of water-free substance was diminished, that of both protein and of carbohydrates rose slightly (the amount of fats was too small to be taken into account), so that the falling off was all in the mineral salts. The experiments do not show the exact increase or decrease in the total amounts of the liquids and their constituents, so that it is impossible to say with entire certainty whether there was or was not an actual gain of protein or fats or carbohydrates. It would seem extremely probable, however, that the liquids received and retained small quantities of these materials from the flesh (bodies) of the animals.
The apparent increase of protein and other materials belonging to the body in the liquids, though slight, is very interesting. I must refer to the detailed account of the experiments for the discussion of it and of the changes in composition of the liquids. The point is that if the changes in composition of the oysters in floating were due to osmose or dialysis alone, we should expect simply a gain of water and loss of salts (and perhaps of soluble carbohydrates). But the flesh seems to have lost a little carbohydrates and fats, and probably protein also, along with the salts, while it was absorbing water, the liquids at the same time gaining more or less of protein and carbohydrates. A way in which this may have come about is suggested by my colleague, Professor Conn, who calls attention to the fact that some mol. lusks, when irritated, produce an extremely abundant secretion of mucus or “slime”-so much, indeed, as to sometimes render a small quantity of water in which the animals may be confined, quite sensibly gelatinous. He suggests that the change to fresh water may induce such a secretion of mucus, and perhaps of carbohydrates and fats as well, as would account for the increase of these substances in the liquids. The observation of oyster-dealers that “water always thickens the natural juices that adhere to the surface of the oyster and makes it slimy,” accords with Professor Conn's statement.
If such secretion did take place, the flesh must probably have lost a little protein during the floating. The estimates of absolute gain and loss of weight of flesh and ingredients are based upon the assumption that the quantity of protein was unaltered in floating. If protein was given off, therefore, the estimates are wrong. But the quantity of protein secreted and the consequent error must be, at most; very slight. If there is an error, its effect would be to make the quantities of nutrients after floating appear larger than they really were. other words, if the error were corrected, it would make the loss of nutritive material in floating greater than it appears to be in the figures above given.
The experiments might have been so conducted as to decide this question of the exact gain and loss of weight of each material in the oysters. It would have been necessary to simply take a larger number in each lot before and after floating, and be certain that the number, weight, and bulk were the same in the floated and not-floated lots of each experiment. For instance, we might, in each experiment, carefully select two lots of, say, a busbel each, as taken from the beds; have the number of oysters the same in each bushel, as an additional assurance that the two lots were alike ; float one bushel, and weigh and analyze both. A few experiments of this sort made under different conditions of time, temperature, kind, and age of oysters, etc., would give very reliable and valuable data. Unfortunately, the means at my disposal did not permit so thorough experiments. I am persuaded, however, that the results of such series of trials, if they could be made and I wish they might be-would be very similar to those of the trials here reported.
It is very interesting to note that these processes of both osmose and secretion which we have been considering in the body of the oyster are apparently very similar to processes which go on in our own bodies-namely, those by which our food, after it is digested, finds its way through the walls of the stomach and other parts of the alimentary canal into the blood, to be used for nourishment. Physiologists tell us that the passage of the digested materials through the walls of the canal is in part merely a physical action, due to osmose, but that it is in part dependent upon a special activity of the cells of the villi. In like manner, the changes in the composition of the oys
ter, if the above explanation is correct, are caused partly by osmose, and partly by special secretive action, the cell-walls and outer coat of the body of the oyster corresponding to the walls of the alimentary canal in the human body. The forms of vital activity in the two cases are different, but osmose is concerned in both.
The main points here urged may be very briefly summarized :
1. In the floating of oysters for the market, a practice which is very general, and is also used for other shell-fish, the animals are either taken direct from the beds in salt water, and kept for a time in fresher (brackish) water before they are opened, or water is added to the shell-contents after they are taken out of the shell. When thus treated, the body of the animal takes up water and at the same time parts with some of its salts, while small quantities of the nutritive ingredients also escape. The oysters thus become more plump, and increase considerably in bulk and weight, but the quantity of nutritive material, so far from increasing, suffers a slight loss.
2. In the experiments here reported, the increase in bulk and weight was from one eighth to one fifth of the original announts. This is about the same as is said to occur in the ordinary practice of floating or “fattening" for the market. According to this, five quarts of oysters in their natural condition would take up water enough
floating ” to increase their bulk to nearly or quite six quarts, but the six quarts of floated oysters would contain about one tenth less of actual nutrients than the five quarts not floated.
3. The gain of water and loss of salts are evidently due to osmose. The more concentrated solution of salts in the body of the animal, as taken from salt water, passes into the more dilute solution (fresher water) in which it is immersed, while a larger amount of the fresher water at the same time enters the body. But part of the exchange, and especially that by which other materials, carbohydrates, protein, etc., are given off in small quantities, is more probably due to a special secretory action.
4. The flavor of oysters is often much improved by the removal of the salts in floating, and they are said to bear transporting and to keep better. When, therefore, the oyster-man takes “good fat oysters which “yield five quarts of solid meat to the bushel ” and floats them so that “they will yield six quarts to the bushel,” and thus has an extra quart, and that a quart of the largest and highest-priced oysters, to sell, he offers his customers no more nutritive material_indeed, a trifle less—in the six quarts than he would have done in the five quarts if he had not floated them. But many people prefer the taste of the floated oysters, and since they buy them more for the flavor than for the nutriment (at ordinary prices, the nutrients in oysters cost the buyer from three to five times as much as similar nutrients in the better kinds of meat), doubtless very few customers would complain if they understood all the facts. And considering that the practice is
very general and the prices are regulated by free competition, the watering of oysters by floating in the shell is, perhaps, less reprehensible than at first thought it might seem. This phase of the question, however, it is not the purpose of this article to discuss.
5. From the standpoint of chemical physiology the most interesting outcome of the experiments is the very interesting parallelism they show between the processes by which the salts and other materials pass from within the body to the surrounding medium and those by which the digested materials of the food in man and other animals are conveyed through the walls of the alimentary canal into the blood and lymph to serve their purposes in nutrition. In each case the process seems to be due in part to osmose (dialysis) and in part to a special function of the organs.
To recapitulate still more briefly: The oysters in “floating” in fresher water, for some hours after they were taken from the beds in salt water, as is commonly done in preparing them for the market, gained from one eighth to one fifth in bulk and weight by taking up water, but at the same time lost about one tenth of their nutritive material. They did this by processes essentially similar to those which go on in our own bodies, and by which the digested food passes from the alimentary canal into the blood, to be used for nourishment.
GEIKIE ON THE TEACHING OF GEOGRAPHY.*
BY FREDERIK A. FERNALD.
in school to be affected by the modern demand that science shall be taught according to the scientific method. It is extremely important that this method of teaching the description of the earth should speedily become general, for most pupils study geography, and those who leave school at an early age may not otherwise obtain that quickening of the powers of observation and inference which the study of science gives.
Furthermore, to quote Professor Geikie, “Geography, in the wide and true sense of the word, offers admirable scope for this kind of training. It may be begun on the very threshold of school-life, and may be pursued in ever-increasing fullness of detail and breadth of view up to the end of that time. No other subject can for a moment be compared with it in this respect. It serves as common ground on which the claims of literature, history, and science may be reconciled.” In order to aid teachers in leading their pupils into the study of
*“The Teaching of Geography. Suggestions regarding Principles and Methods for the Use of Teachers." By Archibald Geikie, LL. D., F. R. S. London and New York: Macmillan & Co. Pp. 202. Price, 60 cents.