COAGULATION (?) OF ZOOIDS. 149 



but not so niarlcedly as the nuclei. If ferrocyanicle of potassium 

 be added to the nuclei shrivelled by acetic acid they swell up 

 and become so indistinct as to be hardly visible. A solution of 

 taurocholate or glycocholate of soda dissolves both nuclei and 

 stroma. A little concentrated NaCl solution also causes the 

 nuclei to disappear. When the corpuscles are washed on a 

 linen filter, a fibrinous- looking mass is obtained, which, on 

 microscopic examination, is seen to consist of shreds of fibrous 

 membrane, or of bundles of fibres, studded with darker spots, 

 and arranged in a manner resembling those of fibrin, though 

 more regular and with less intercrossing. These spots seem to 

 be the nuclei, but their outline is not so distinct, nor do they 

 take the deep tint with aniline which they do in the powdery 

 condition, the fibres becoming quite as deeply tinted as they. 



The zooids are insoluble in water, and when suspended in 

 it sink very slowl}', but do so much more quickly after the 

 addition of alcohol, concentrated acetic or oxalic acid, or dilute 

 mineral acids. The mixture with water is quite mobile, and 

 does not foam when shaken ; but does so after the addition of a 

 little NaCl solution, becoming at the same time somewhat tena- 

 cious and much clearer, the nuclei being partly dissolved and 

 partly suspended. A concentrated mixture with NaCl solution 

 gives a white flocky precipitate when much diluted. Salt solu- 

 tions, of even one-fourth per cent., dissolve them to a consider- 

 able extent. The solubility in NaCl solution varies much, 

 diminishing when the zooids stay long in water, but more 

 slowly when the temperature is low. The same is the case 

 with mucin obtained from tendons. 



When many zooids are suspended in water, one drop of con- 

 centrated solution of potash or soda is sometimes sufficient to 

 convert 40 cubic centimetres of the mixture from a milky 

 mobile liquid to a clear gelatinous mass, resembling albuminate 

 of potash in appearance, though not quite so firm. When this is 

 thrown on a filter, the filtrate gives no precipitate with acetic- 

 acid. When more potash is added, a tenacious ropy fluid is 

 produced, which filteis very slowly ; the filtrate is mobile, and 

 though generally more or less alkaline, is sometimes neutral. 



Alkaline carbonates dissolve them, but much more slowly, 



