452 CALCIFICATION, CONCRETIONS, AND INCRUSTATIONS 



among the diseases that depend upon specific deficiencies in the diet, 

 especially the fat-soluble "vitamines" which cod-liver oil supplies 

 abundantly. So far, however, this hypothesis is not positively estab- 

 Jished.^^ (See also Rickets, under ''Deficiency Diseases" Chapter xii.), 



CONCRETIONS 



All pathological concretions appear to be laid down according to a 

 definite law. There must first be a nucleus of some substance differ- 

 ent from the substance that is to be deposited, and which is most 

 frequently a mass of desquamated cells, but may consist of clumped 

 bacteria, masses of mucus, precipitated proteins, or a foreign body of 

 almost any sort. Upon this nucleus substances crystallize out of 

 solution, much as cane-sugar crystallizes on a string to form rock 

 candy, but with the important exception that among the crystals is 

 usually deposited more or less mucin or other organic substance, which 

 forms a framework in which the crystals lie, and which remains, if the 

 crystals are dissolved out, as a more or less perfect skeleton of the 

 concretion. In no case would the concretion form were it not that 

 the solution is overcharged with some substance, but not infrequently 

 it is the presence of the nucleus that leads to the precipitation of the 

 substance; i. e., the nucleus may play either a primary or a secondary 

 role. With few exceptions, the dissolved substance is deposited in 

 crystallme form, although the crystalline structure may in time partly 

 disappear through condensation or through filling of the interstices 

 with some other material. Even so structureless a substance as 

 amyloid may, when forming concretions, appear in a crystalline form 

 (Ophiils). The structure of a concretion depends upon two factors: 

 The crystals tend to be deposited at right angles to the surface, and 

 thus give a radiating structure; but the rate of deposition is usually 

 irregular, and during the periods of quiescence the surface tends to 

 become covered with mucin or other organic substances, hence we also 

 get a concentric, laminated structure. Frequently both of these lines 

 of formation are easily discerned, but either one or the other may be- 

 come obscured. 



Concretions consist, therefore, of mixtures of colloids and crystal- 

 loids deposited from solutions of the same character, and hence the 

 application of the principles of colloidal chemistry throws much 

 light on the conditions of their formation."'''^ Colloidal solutions 

 hold in solution greater quantities of crystalloids than simple solutions, 

 for the reason that at the surface of each colloidal particle there is a 

 zone in which the crystalloids are more concentrated than elsewhere, 

 thus permitting more crystalloids to be dissolved in the solvent 



""^ See Paton, Findlay and Watson, Brit. Med. Jour. Dec. 7, 1918; Mellanbv* 

 Lancet, 1919 (196), 407. 



^6 See Schade, Munch, med. Woch., 1909 (5G), 3; 1911 (58), 723; Zeit. exp. 

 Path., 1910 (8), 92; also Lichtwitz, Ergeb. inn. Med., 1914 (13), 1; also his mono- 

 graph "Ueber die Bildung der Ilarn- und Gallensteine," Springer, Berlin, 1914. 



