The edible Bird's-nest, or Nest of the Java Swift (Collocalia Nidifica)

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J. R. Green
THE swifts as a family are remarkable for certain peculiarities in the construction of their nests, fastening together the materials they use by a peculiar kind of secretion. The nest of the common swift of our own country has at -least its innermost layer so agglutinated. Collocalia faciphaga, according to Bernsteiin, fastens together in this way the whole of the structure. Perhaps the nmost interesting of the whole genus is C. nidifica, a species met with in Java and Borneo, concerning the construction of whose habitation much controversy has taken place. This species produces the so-called edible bird’s-nest, a delicacy long leld in high esteem by the Chinese and lately brought into prominence in England through the Health Exhibition at South Kensington last year. The nest is in appearance not unlike a dried flattened spongy bone such as the occipital bone.

It has a brownish or dirty white colour; is on the outside compact and hard; on the inside spongy in texture. It is brittle, breaking with conchoidal fracture, much like glue.
Three chief hypotheses have been advanced as to its construction. The first is that it is partly at least of vegetable origin consisting of pieces of alga fastened together by the bird’s saliva. The caves which the birds are found to haunt have their sides covered in places with a peculiar alga allied to Gleocapsa, the diffluent cell-walls of which would easily lend themselves to such a use. The advocates of this view suggest also as a likely material certain marine algae. In the nestbuilding season the birds are observed often to settle at the edge of the shore and to return thence directly to their caves. The nest of the nearly allied C. fuciphaga, which much resembles that of C. nidifica in -appearance, is according to Bernstein’ built up of plant stalks, stems J. R. GREEN. says that in the stomachs of the birds at the breedingr season, nothing but insects can be found, showing that they do not use in the building regurgitated vegetable matter. In a specimen’ of the nests used for soup at the late Health Exhibition, btut little structure of any kind was visible. The appearance of the nest as found in the caves has been described above. In its natural condition the material was too hard and brittle for microscopic investigation. Prolonged soaking in water or glycerine caused it however to swell up without losing any peculiarity of its form. It became soft and almost gelatinous in texture and was then easy to examine. Under a low power of the microscope it appeared to be laminated; striae were visible over its surface, parallel, or nearly so, and somewhat wavy. On teasing it with needles it readily split in two directions, one parallel with, the other at right angles to, the surface. The most careful examination with both low and high powers failed to show the presence of vegetable cells or of any debris arising from such. The only structural elements at all to be identified wvere bodies closely resembling in appearance sqtuamous epitheliuni cells. These occurred scattered about in the substance, but only on the surfaces of the laminae into which it readily split. Microchemical reagents were equally unable to show any traces of vegetable origin. The material stained pale yellow with iodine, but in adding sulphuric acid, there was no developnment of the blue colour which under such treatment demonstrates the presence of cellulose. There was considerable swelling up under the action of the strong acid, but no further structure was brought out thereby. Similar results followed the application of chlor.-zinc-iod. or Schultze’s solution, the swelling being however much slower. The application of nitric acid, followed by ammonia, produced an orange colour apparently identical with that given on similar treatment by proteid bodies. Examination of sections cut in three planes revealed no further structure. The sections stained readily with haematoxylin but not with carmine or picro-carmine. The substance reduced solution of argentic nitrate with appearance of the well-known brown colour. With both the stains that affected it, the whole of the section was Rniformly coloured. 42The microscopic investigation of the properties of the nest pointed thus to the third view of its formation quoted above. But little concerninog the chemical nature of the material has hitherto been I Kindly placed in nmy hands by Dr Sclater, FJR.S. EDIBLE BIRD’S NEST. 43These reactions, considered together with the absence of structure in the material, point evidently to its being the product of the activity of some gland in the body, and bear out the view advocated by Sir E. Home and by Bernstein. It does not appear however from them whether the gland is a peptic or a salivary one. Evidence on this point is not forthcoming so far, for the most careftil examination has failed to show any ferment-property attaching to the nest. Neither the first water in which it was soaked, nor its solution in lime water, nor the swollen up material itself, was able to convert starch into sugar, nor was any action on fibrin found to take place, whatever the reaction. It J. R. GREEN. 44Though decomposed by sulphuric acid the nest was not acted uipon in the cold by weak hydrochloric acid, 1-5o/o, or by alkalis. On boiling with NaHO it was dissolved, to a brown solution. On considering these reactions and decompositions it is impossible to avoid being struck by the resemblance which the nest substance shows to the mnuoin described by Eichwald’ as occurring in the tissues of Helix pomatia and by Obolensky as found in the secretion of submaxillary glands’. The chief differences are 1. The nest is insoluble in 5V/0 HCl and in dilute alkalis, while mucin is soluble in both. 2. Mucin in solution is precipitated by acetic acid, while the nest solution only becomes opalescent. 3. Mucin is indigestible by pepsin, while the nest substance is dissolved, though with extreme slowness. 4. Mucin in solution in NaHO yields to ether a body which is coloured green by ferric chloride1. The nest material does not. By both microscopical and chemical examination therefore the theory of vegetable origin is unsupported. The substance is an animal product, so closely allied to mucin that it may be said to be a variety of it; and it is hardly open to doubt that it is the result of the activity of the glands described by Bernstein2 as being remarkably developed in the nest-building season and as atrophyingf immediately afterwards. 1 Obolensky, loc. cit. 2 Loc. cit.