GROWTH, METAMORPHOSIS AND DEVELOPMENT 269 



calcium when he placed pieces of cartilage in chlorid of lime solution. 

 This suggests the method by which lime is deposited in damaged 

 tissues (vessel walls or tubercles). We must also consider the 

 simultaneous precipitation of positively and negatively charged 

 albumin with the breaking down of calcium salts as we shall describe 

 later when we discuss concrement formation at greater length (see 

 p. 271 et seq.). 



Finally, we may consider some kind of specific adsorption by 

 definite cell groups. We might also consider the mutual precipita- 

 tion of positively and negatively charged albumin which carry salts 

 down with them in the same way as is more fully described in the 

 case of concrement formation (p. 271 et seq.). 



What has been said here of bones also holds, of course, equally well 

 in principle for the shells of molluscs and snails, for the armor of 

 crustaceans, as well as for other ossification phenomena. Morphol- 

 ogists distinguish primarily between calcification and ossification (see 

 GEBHARDT) . In lower animals (shells of snails and mussels, carapace 

 of crabs, spicules of sponges, etc.), the lime salt occurs chiefly in 

 microcrystalline form, as fine granules in the calcifying tissues. In 

 contrast with this calcification, lime forms an optically completely 

 homogeneous deposit in bone and never occurs as a formed or 

 crystalline precipitate. Possibly this essential difference depends on 

 the fact that special cells, osteophytes, take part in bone formation. 

 It is still impossible for colloid research as yet ? to offer even an- 

 hypothesis in explanation of this difference. 



R. LIESEGANG* (his correctness in doing so, I shall not discuss) 

 criticises an explanation of ossification which involves the presence 

 of special cells, the osteoblasts. He calls attention to the fact that 

 deposits of lime occur in places where there are no osteoblasts, as in 

 the arterial wall, in arteriosclerosis, or in brain cells. He evidently 

 concludes that under some circumstances, even without a special 

 storing- up, it is possible to have a precipitation from blood serum 

 supersaturated with calcium salts, in which action the formation of 

 centers or nuclei possibly take part (similar to the theory of H. 

 BECHHOLD and ZIEGLER* S for the deposition of urates). 



The very marked density and the poverty of the bony framework in 

 organic substances is deserving of special consideration. For this, 

 the investigations of R. LiESEGANG* 2 offer valuable experimental 

 support. He showed that when calcium phosphate membranes 

 were allowed to form in gelatin jellies (by the diffusion of disodium 

 phosphate and calcium chlorid towards each other), that they were 

 almost free from gelatin; to a certain extent the organic supporting 

 substance had been forced away. 



