dcTOBM 1, 1885.] THE TROPICAL AGRICULTURIST. 



agg 



on so as to be readily removed. Its principal feature 

 consists in the inlut Ibrough wLic-li the hquid is forced 

 being bored tangeutially through its wall, so as to 

 cause a rapid whirling or centrifugal motion of the 

 liquid which issues in a funnel-shaped spray through 

 a central outlet in the adjustable cap. — Prof. Eiley in 

 American Entomohgiit. 



EDIBLE BIRDS' ; NESTS. 



The nature and composition of the edible birds, 

 nests of which eve-youe has heard, and which any 

 visitor to the International Health Exhibition at 

 South Keusiugton might have tasted if he pleased, 

 is a problem the solution of which has puzzled 

 naturalists as much as did at one time the question 

 concerniufr whitebait. 



The nests in question, so much prized by the 

 Chinese, are made, as mo.st people are aware, by a 

 species of cave-haunting swift of the genus CoUocalia, 

 which breeds in colonies, in caverns sometimes by the 

 sea, sometimes inland, according as they are foimd 

 suitable for the purpose. They are to be found in 

 India, Ceylon, Borneo, and Java, and we have seen 

 some very perfect nests of the kind which were brought 

 from the Andaman Islands. Mr. E. L. Layard has 

 described the appearance of a cave tenanted by these 

 birds in the breeding season in Ceylon; and Mr. AV- 

 B. Fryer has published an equally interesting account 

 of a visit which he paid to the so-called "Birds-nest 

 Caves" at Gomanton in North Borneo, where hundreds 

 of the nests were to be seen glued, as it were, to 

 the sides of the cave, many of them at a considerable 

 height, from which they were detached by the natives 

 with the aid of light bamboo ladders. The formation 

 of the nests differs. Some appear to be formed of 

 flakes or threads cemented together, making an 

 almost solid nest; others are composed entirely of 

 viscous matter. The exterior exhibits many nearly 

 straight threads, which incline or are attached to 

 each other ; the interior, which is rather shallow, 

 shows many layers of irregular network, formed of 

 a multitude of threads that cross and recross each 

 other in every direction. 



The best— that is to say, the whitest and cleanest- 

 are of a semi-transparent fibrous texture, having the 

 .appearance of being foimed of isinglass. Those less 

 sought after are much discoloured, sometimes almost 

 :black, and are iutermised with dry grass, hair, or 

 -leathers. The question which naturalists have sought 

 to determine is '• how the nest is made, and of what 

 it is composed T' Several theories have been advanced 

 on the subject, and different observers have professed 

 to detect in its structure either a vegetable origin 

 from seaweed or fungus, or an animal origin from 

 agglutinated and dried fish spawn, or the hardened 

 saliva of the bird itself, produced iu large quantities 

 from special glands secreting it. Mr. Pryer, who has 

 collected a great number of these nests in Borneo, 

 says (Zooloqist, 1SS5, p. 46): "The nests are made 

 from a sort of fungoid growth that iucrusts the 

 limestone in all damp situations. It grows about an 

 inch thick, outside dark bhowu, but inside white. 

 The birds make the black nests from the outside 

 layer, and the best quality of white nests are of 

 course from the inside. It is taken by the bird in 

 the mouth and drawn out in a filament backwards 

 and forwards like a caterpillar weaving its cocoon," 



Upon this statement Mr. G. Murray remarks {Zoolof/!st, 

 1885, p. 147) : " The alga of microscopic dimensions 

 found by Mr. Prytr in the cave inhabited by the 

 swifts which build the edible nests is an undescribed 

 species of Crococcus. The members of the group to 

 which it belongs are very commonly found growing 

 on the walls ot caverns. In this case the incrustation 

 produced b> the accumulation of the algse is of 

 unusual thipkneiju„-!d of horny consistency when dry, 

 but turns pulpy when taaked in cold water. On the 

 outer surlace there is a dark layer (black to the 

 naked eye, but very dark greenish yellow when 

 viewed with the microscope,) consisting of the living 

 jilga, Beneath this outer dark layer the mass of the 



incrustation is white, and consists of a dense accumul- 

 ation cf innumerable dead bodies of the sdgx, the 

 structure of which is barely distinguishable. In none 

 of the edible ne=t- which I have examined, however, 

 is there any trace of an alga, and it appears to le 

 definitely settled that these are constructed from 

 materials which are the intrinsic product of thn 

 bird. Jlr. Pryer states his opinion that certain nests 

 are made from the bbtck outer layer of the incrustation. 

 If such a nest were examined, it would give conclusive 

 evidence either way, since the black layer, as just 

 mentioned, consists of living algw, the structure of 

 which would be far more readily di-cernible than 

 the traces of the white pirt of tho incrustation." 



We do not know whether Mr, Pryer has seen this 

 note, being, we believe, still in Borneo, but iu a 

 further communication of his own, which has since 

 been published (Zooloyist, 1885, p. 29S), he appears 

 to have altered his former opinion on the subject, 

 for he says, "With regard to the material from 

 which the nests are made, I regard the algffi theory 

 with great doubt. The natives say the birds skim 

 up froth or scum from the water, and use it as the 

 material. I myself think it is simply a natural 

 secretion of the birds themselves." That is to s.iy, 

 he adopts the view expressed by Mr. Murray, and 

 before him by Dr. Jerdou "(Birds of India"), BIyth, 

 and Sir Everard Home. 



Dr. .Jerdon writes : " The nest, when pure and of 

 the first make, is composed entirely of inspissated 

 mucus from the l.atge salivary glands of the bird.'. 

 In a posthumous article on the Oypselid;e, published 

 in the Zoologist, 1884 (pp. 300-327), the late Mr 

 BIyth observes : " The animal origin of the edible 

 nests is at once detected by simply burning a bit 

 of one ; and Mr Laidlay informed us that, upon 

 analysis, he found the constituent elements to be 

 those of inspissated saliva." Sir Everard Home, so 

 long ago as 1817, published the results of a dissection 

 made by him ot a specimen of the bird (CoUocalia 

 nidifica) from Java (Phil. Trans 1817, p. 3o7), 

 wherein he described a peculiarity iu the gastric 

 glands, pointing out that a membranous tube surrounds 

 the duct of each gland, which, after projecting a 

 little way into the gullet, splits iuto separate portions 

 hke the petals of a flower, and suggesting that the 

 material of which the nest is composed is secreted 

 by the surfaces of these tubes just as the gastrip 

 juice is secreted by the glands themselves. 



One of the latest writers on the subjict is Mr J, 

 R. Green, of Trin. Coll,, Camb,, who in an article iu 

 the Jonrmd of Phi)siology for April last, after quotiug 

 Sir Everard Home's views, points out that they have 

 since been confirmed by Dr Bernstein (Journal jiir 

 Ornitiioloyie, l^o'.), p. Ill), who found in CoUocalia 

 nidifica two large salivary glands, which secrete 

 mucus in large quantities. He then proceeds to detail 

 the results of a microscopical and chemical exan in- 

 ation made by himself of a specimen of the nests 

 used for soup at the International Health Exhibition. 



The most careful examination, he says, with both 

 low and high powers, failed to show the presence of 

 vegeiab'e cells, or of any dihris arising from .such ; 

 while the chemical tests applied appeared to him to 

 indicate that the material of which the nest Is formed 

 is the product of the activity of some gland iu the 

 body, which bears 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, says Mr. Green, Is not 

 forthcoming so far ; for " the most careful examination 

 has failed to show any ferment property attaching 

 to the nest." The result of Mr. Green's experiments, 

 nevertheless, sufficiently refute the tlieory of xeriftahk 

 origin, and support his view that the substance in 

 qUHstion is au animal product closely allied to mutm, 

 and is derived from glands which are remarkably 

 developed in the nesting season, as remnrked by 

 Bernstein, and afterwards become atrophied. 



Capt. Lewis, who saw much of the.=e birds iu the 

 Nicobar Islands, states that the edible uests, as we 

 8«e them, are only the lining, which eoto^ put entjr 



