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

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J. R. Green
THE EDIBLE BIRD’S-NEST, OR NEST OF THE JAVA SWIFT (COLLOCALIA NIDIFICA). BY J. R. GREEN, B. Sc., B.A., Scholar of Trinity College, Cambridge. 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 1 Journtalfur Ornitihologie, 1859, p. 111.
EDIBLE BIRD’S NEST. of Casuarina, stalks of grass &c., placed nearly parallel on one another and glued together by a peculiar horny substance. It has been sugaested by some observers that the birds do not merely glue the vegetable matter together, but that it is eaten and after partial digestion is again ejected and in that condition is made to form the substance of the nest. The second theory is that the material is made by the bird from fish spawn, or collected from the mollusca picked up upon the surface of the sea. The third hypothesis worthy of notice was advocated by Sir Everard Home in a paper written in 18171. It is that the material consists entirely of an animal secretion and that it is essentially the product of certain glands occurring in the bird. Sir Everard describes in the Java swift a peculiar construction of the gastric glands. He says that there is a membranous tube surrounding the duct of each gland which after projecting into the gullet a little way, splits into separate portions like the petals of a flower; and he suggests that the material of which the nest is composed is secreted by the surfaces of these tubes just as the gastric juice is secreted by the glands themselves. This internal origin is also advocated by Bernstein, who wrote in 18592. After describing the appearance of the nest and stating what views were held upon the stubject of its construction, he speaks of certain structural peculiarities of C. nidificca with which he connects the secretion. He says that he has found in the bird duiring the nestbuilding season two large salivary glands forming cushions by the side of the tonague, which secrete mucus in large quantities. This collects in the front of the mouth under the tongue near the ducts of the glands, and resembles very much a concentrated solution of gum arabic, being 41
so viscid that it can be drawn out of the mouth in the form of threads. When dry its appearance is exactly that of the nest material. Of these three views of its formation the first and third have met with most support. It should not be difficult to decide between them, because if the vegetable theory be correct, the microscope should reveal cells, or traces of cells, which could be referred to whatever alga had been used, while chemical tests for the presence of cellulose are not difficult to apply. Trecul and Montagne8 writing in 18a5 declare their inability to recognise evidence of such origin and Bernstein4 in 1859 says no traces of plant cells so far had been found to be present. He further 1 Phil. Trans. 1817, p. 337. 2 Loc. cit. 3 Contpt. rend. Ac. Sc. 1855. 4 Loc. cit.
J. R. GREEN. says that in the stomachs of the birds at the breedingr season, nothing but insects can be found, showi42
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. The 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 EDIBLE BIRD’S NEST. published. In his paper’ Sir Everard Home describes what had been ascertained on this bead in 1817. From his investigations he held it to consist of a substance ” having properties intermediate between gelatine and albumen.” It has already been stated that under prolonged soakino in water or in glycerine it swelled up without losing its form, and became semigelatinous in texture. In neither warm nor cold water was it soluble: resisting a maceration even of six weeks in the latter without decomposition. On transferring it thence to lime or baryta water it slowly dissolved, revealing as it did so certain foreign bodies, d4bris &c. mechanically entangled in its laminae. The chief part of this, which altogether was in very small quantity, consisted of small feathers. The solution so obtained presented the following characteristics:1 On adding acetic acid there was a very marked opalescence at once, but this did not become a precipitate even on standing and warming. 2. Alcohol gave a bulky flocculent precipitate of pinkish colour. 3. There was a well-marked xanthoproteic reaction. 4. There was no reaction whatever with Millon’s reagent. 5. There was no further precipitate on adding potassic ferrocyanide to the solution made opalescent by acetic acid. 6. Lead acetate gave at first a white precipitate. On standing, a quantity of thin plates resembling crystals separated out. On washing these and adding sulphuretted hydrogen they turned brownish-black. When the reaction of the solution was made faintly acid, the lead acetate did not give a precipitate, but only rendered it opalescent. The liquid did not reduce Fehling’s fluid. These 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 1 Loc. cit.