We have thus far followed the food through the intestine, the circulation and the excreting organs, but, as I mentioned before, all our tissues live in a fluid medium, namely, the lymph in which they are bathed and not in the blood which circulates through them. The lymph passes through the capillaries from the blood into the lymph spaces. Here it nourishes the tissues, and after it has fulfilled its office it is either re-absorbed into the venous radicals or conveyed by the lymphatics directly into the larger veins. Various substances have the effect of quickening the flow of lymph from the blood into the lymphatic spaces. Amongst these are : egg-albumin, Witte's peptone, extract crayfish, mussels and leeches, nuclein, urea, sugar and salts.
It is probable that a number of others have also this action, and it has lately been found that it is possessed to a large extent by strawberries. The effect of such substances on tissue-metabolism in health and disease is at present unknown, sometimes it may be for good, at other times for harm. I once saw a patient who had some obscure disease which resembled pernicious anaemia more than anything else. Drugs seemed to do little good, but many strawberries eaten all through the day produced very marked benefit. On the other hand I knew a lady in whom the power of strawberries to quicken the effusion of lymph was so great that a single strawberry produced such swelling of the eyelids as almost to blind her.
Salts of potash and soda have a lymphagogic action, and when it is desirable to lessen the exit of lymph from the blood vessels, as in the dropsy of cardiac disease, a diet free from sodium chloride is frequently useful. Calcium salts have an opposite action and lessen the flow of lymph into the lymph spaces. Magnesium appears to have a similar effect, and thus salts of these metals are useful in oedema and localized lymphatic swelling such as urticaria.