HARTING'S CALCO-GLOBULDsE HOI 



ostrich and cassowary this concretionary layer is of considerable 

 thickness ; and vertical as well as horizontal sections of it are very 

 interesting objects, showing also beautiful effects of colour under polar- 

 ised light. And from the researches of Professor W. C. Williamson 

 on the scales of fishes, there can be no doubt that much of the 

 calcareous deposit which they contain is formed upon the same plan. 

 This line of inquiry has been contemporaneously pursued by 

 Professor Harting, of Utrecht, who, working on a plan funda- 

 mentally the same as that of Mr. Rainey (viz. the slow precipitation 

 of insoluble calcium salts in the presence of an organic 'colloid'), 

 has not only confirmed but greatly extended his results, showing 

 that with animal colloids (such as egg-albumen, blood-serum, or a 

 solution of gelatine) a much greater variety of forms may be thus 

 produced, many of them having a strong resemblance to calcareous 

 .structures hitherto known only as occurring in the bodies of animals 

 of various classes. The mode of experimenting usually followed by 

 Professor Harting was to cover the hollow^ of an ordinary porcelain 

 plate with a layer of the organic liquid to the depth of from O4 to 

 0*6 of an inch, and then to immerse in the border of the liquid, 

 but at diametrically opposite points, the solid salts intended to act 

 on one another by double decomposition, such as calcium chloride, 

 nitrate, or acetate, aiid potassium or sodium carbonate; so that, 

 being very gradually dissolved, the two substances may come slowly 

 to act upon each other, and may throw down their precipitate in the 

 midst of the ' colloid. 1 The whole is then covered with a plate of glass, 

 and left for some days in a state of perfect tranquillity ; when there 

 begins to appear at various spots on the surface minute points re- 

 flecting light, which gradually increase and coalesce, so as to form a 

 crust that comes to adhere to the border of the plate ; whilst another 

 portion of the precipitate subsides, and covers the bottom of the 

 plate. Round the two spots where the salts are placed in the first 

 instance the calcareous deposits have a different character : so that 

 in the same experiment several very distinct products are generally 

 obtained, each in some particular spot. The length of time requisite 

 is found to vary with the temperature, being generally from two to 

 eight weeks. By the introduction of such a colouring matter as 

 madder, logwood, or carmine, the concretions take the hue of the 

 one employed. When these concretions are treated with dilute 

 acid, so that their calcareous particles are wholly dissolved out, 

 there is found to remain a basis substance which preserves the form 

 of each ; this, which consists of the ' colloid ' somewhat modified, is 

 termed by Harting calco-globuline. Besides the globular concretions 

 with the peculiar concentric and radiating arrangement obtained 

 by Mr. Rainey (fig. 817), Professor Harting obtained a great 

 variety of forms bearing some resemblance to the following : 1. The 

 *' discoliths ' and * cyatholiths ' of Huxley. 2. The tuberculated 

 'spicules' of Alcyonaria, and the very similar spicules in the 

 mantle of some species of Doris. 3. Lamella? of 'prismatic shell - 

 substance,' which are very closely imitated by crusts formed of 

 flattened polyhedra, found on the surface of the ' colloid.' 4. The 

 spheroidal concretions w r hich form a sort of rudimentary shell within 



