Fifty years in the past the late Jim Linzell and I have been writing our monograph, Salt Glands in Birds and Reptiles, for the Physiological Society’s Monograph Collection; it was revealed in Might 1975. On this sequence I revisit among the subjects and individuals who adopted up the invention of salt glands in birds by Knut Schmidt-Nielsen.
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One drawback with writing a guide 50 years in the past was that the copy that arrives within the reader’s arms has a way of finality. Final ideas, modifications of thoughts or new proof can solely be handed on by producing a brand new version some tears later or masking the identical floor in an invited overview. That drawback, though nonetheless current, is lessened by having a web site masking a selected publication that may be amended accordingly.
One level we forgot to say once we wrote Salt Glands in Birds and Reptiles was the chance that secretion from different glands might maybe be mistaken for secretion from the nasal salt glands of birds. Small drops or dampness seen inside the nostril in response to cholinergic medicine or during times of pleasure could possibly be interpreted as an indication of the salt gland being activated at a low charge or for a quick interval. Nevertheless there stays the chance, significantly if the secretion that appeared was not analysed, that the small quantities might come up from different glands within the head, the secretions from which might discover their approach to the nostrils.
The Harderian gland is a comparatively massive gland that sits behind the eyeball. It’s significantly related to tetrapods which have a nictitating membrane. A lot of capabilities of its secretion have been described or postulated together with, after all, lubrication and safety, together with immunoprotection, of the attention. Briefly, it’s a second supply of tears, alongside the lachrymal gland which in birds could be very small. Simply as once we cry, tears seem not solely from the attention itself but in addition move down the nasolacrimal duct to the nostril; sniffling and lachrymosity go collectively.
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| We reproduced this drawing in Salt Glands in Birds and Reptiles I’ve added colouring to point out the nasal salt gland and the Harderian Gland |
There isn’t any indication that in birds with a nasal salt gland that the Harderian gland performs any half in eradicating extra salt. In geese, for instance, we discovered no proof for any enhance in blood circulation by way of the Harderian gland. In contrast, salt gland blood circulation elevated elevated as much as 26-fold when secretion was activated by a salt load. Nevertheless, there’s one intriguing report within the literature that the Harderian gland may be doing one thing in relation to salt and water stability in some birds.
In 1968 the late Maryanne Robinson Hughes and Frank E Ruch of the College of British Columbia seen that in home geese saved on sea water the feathers between the beak and the attention have been moist and contained depressions which have been stuffed with a transparent fluid. Evaluation of the fluid confirmed the sodium focus to be much like that of blood plasma. Nevertheless the potassium focus was a lot greater than that in plasma. Furthermore, the potassium focus elevated with greater salinities as much as full energy sea water, the principle rising occurring when the salinity of the water exceeded that of plasma. No such impact was seen in gulls and the suggestion was that geese dwelling on sea water are at a precarious state of salt and water stability in contrast with gulls which might address the salinity of sea water far more readily. Though the supply of the potassium-rich tears was not recognized, the Harderian gland is the most definitely since for the reason that lachrymal glands are tiny, just one hundred of the load of the Harderian glands.
Pertinent to the purpose of this text is that it was inconceivable to find out simply how a lot potassium the Harderian glands have been secreting within the geese since tears could possibly be passing down the nasolacrimal duct. Nevertheless, they did discover a band of easy muscle across the opening of this duct which they instructed might act as a sphincter regulating the passage of tears from the attention by that route.
If solely we had talked about it on the time I might not have wanted to jot down this text 50 years later.
Fänge R, Schmidt-Nielsen Okay, Robinson M. 1958. Management of secretion from the avian salt gland. American Journal of Physiology 195, 321-326.
Hughes MR, Ruch FE. 1969. Sodium and potassium in spontaneously produced salt-gland secretion and tears of geese, Anas platyrhynchos, acclimated to recent and saline waters. Canadian Journal of Zoology 47, 1133-1138.
Peaker M, Linzell JL. 1975. Salt Glands in Birds and Reptiles. Cambridge: Cambridge College Press.