CONCRETIONS. 



[ 196 ] 



CONFERVA. 



CONCRETIONS and CALCULI. 



These terms are rather indefinite. A hard 

 body of comparatively considerable size, 

 formed within an animal organism, would 

 be called a calculus, whilst a body of con- 

 siderable comparative size in which hard- 

 ness was not a marked feature, or a hard 

 body of small or microscopic dimensions, 

 would be called a concretion. Under the 

 latter term, the notion of a compound 

 structure is usually implied. Calculi gene- 

 rally consist of various organic and inor- 

 ganic substances entering into the compo- 

 sition of the secretions of the body, which 

 are precipitated from various causes. Those 

 found in the intestinal canal are mostly 

 composed of undigested vegetable tissues 

 derived from the food. Most, if not all, 

 calculi and concretions are mixed with ani- 

 mal matter (proteine-compounds) derived 

 from the mucous cavities in which they are 

 contained, or simultaneously precipitated, 

 with their characteristic compounds, from 

 the secretions in the midst of which they 

 are formed. Hence when the proper cal- 

 culous matter is dissolved by a reagent 

 which exerts little or no action upon the 

 animal matter, a mass is left whicn exhi- 

 bits the form of the original body ; and the 

 organic cast often so resembles a cell, that 

 some hasty observers have attributed to 

 calculi a cell-origin. 



Calculi and concretions enlarge by the 

 deposition of new matter upon their outer 

 surface ; and as this deposition is not uni- 

 form and uninterrupted, either in regard to 

 the nature or proportion of the respective 

 constituents, they mostly exhibit a lami- 

 nated structure. This is visible to the 

 naked eye in the larger ones, and evidenced 

 in those which are microscopic by the ap- 

 pearance of concentric rings, and of a 

 nucleus or nuclei. These concentric rings 

 and nuclei are distinguishable equally in 

 concretions formed artificially as in those 

 occurring naturally. 



The inorganic matter in concretions is 

 in the crystalline state, the crystals being 

 usually small, granular or radiate, and in- 

 termingled with the organic substance ; 

 which arrangement is conveniently ex- 

 pressed by Ehrenberg's term "crystalloid." 

 The crystalloids have a great resemblance 

 to cells, for which they have often been 

 mistaken. 



BIBL. Taylor, Hunt. Catalogue, Calculi ; 

 Quekett, Med. Times, 1851, xxiv. 551 ; 

 Grifiith, Med, Times and Gaz. 1852, xxv. 



272; Rainey, Medico- Chir. Rev. 1857, 

 and Qu. Mic. Jn. 1858; Meckel, Mikro- 

 geologie. 



CONDENSER, ACHROMATIC, BULL'S- 

 EYE, &c., for opaque objects. INTRO- 

 DUCTION, pp. xix & xx. 



CONFER'VA, Plin. A genus of Con- 

 fervacese (Confervoid Algse), which, as 

 restricted here, contains chiefly marine 

 species ; but we have thought it advisable 

 to retain in it the species separated by 

 Kutzing as Chcctomorpha and by Thuret as 

 Microspora ; so that our Conferva corre- 

 sponds to HassalTs proposed genus Apia- 

 nema. The plants consist of unbranched 

 filaments, composed of cylindrical or moiii- 

 liform cells, the length and diameter of 

 which have a very variable relation in dif- 

 ferent species, and containing starch-gran- 

 ules. The species with nioniliform cells 

 form Kiitzing's Glceotila. They are repro- 

 duced by zoospores formed from the cell- 

 contents. Braun says that C. bombycina 

 produces four in a cell. According to 

 Thuret, C. area produces large numbers, 

 which escane by a lateral orifice ; while the 

 species he describes as Microspora floccusa 

 forms a number which escape Dy a circular 

 dehiscence breaking up the filaments. The 

 zoospores are 2-ciliated in general, but 

 sometimes bear four. The spores have not 

 been observed; and hence Kiitzing has sug- 

 gested that the Conferva may be sterile 

 forms of (Edogonium ; but the true CEdogo- 

 nia produce solitary zoospores with a 

 crown of cilia. Ratenhorst describes 30 

 species. British species : 



Freshwater. 



C. bombycina, Ag. Filaments 1-3GO to 

 1-180" in diameter, four or five times as 

 long, forming a yellow-green cloudy stra- 

 tum. Common in stagnant water. Dillw. 

 Conferva, pi. 60. 



C.floccosa, Ag. (PI. 9. fig. lib). More 

 robust ; articulations once or twice as long 

 as broad. Microspora floccosa, Thuret, 

 Ann.des Sc.Nat. 3 ser. xiv. pi. 17. figs. 6,7. 



Marine. 



Thirteen species are described by Harvey 

 (Mar. Alga), of which C. area, Dillw., is 

 one of the commonest, remarkable for the 

 large size of the tufted filaments, as thick 

 as hog's bristles, growing 3 to 12" long, of 

 a yellow-green colour. C. Melagonium, 

 Web. and Mohr, has erect tufted filaments 

 equally thick ; while C. Linum, Roth, has 



