$. III. DIST. CHAR. Mode. 55 



b. 7. INTROMISSION (Intromissio). In which 

 substitution takes place during the removal of the or- 

 ganic particles the mineral being gradually in- 

 troduced into the animal or vegetable body., sup- 

 plying the place,, and taking the form of the matter 

 lost. By this mode, the internal fabric, as well as 

 the external figure, of the original is preserved. 



Obs. The change induced by intromission is 

 usually supposed to have been carried on as follows 

 By putrefaction the principles of organic bodies 

 are gradually liberated If the putrid fermentation 

 take place in an animal or vegetable substance., ca- 

 pable of retaining its form,, after the commencement 

 of the process, and to which water, holding mineral 

 matter in solution, has free access,,f the dissipation 



species of fossil shell, or other like body, would in most instances 

 furnish three separable species of reliquia; i. e. the impression 

 of the external surface on the enclosing matrix, the body itself \ 

 petrified or in the state of a conservatum, and the nucleus, bear- 

 ing the impression of the concave or interior form. Nuclei, there- 

 fore, we merely consider as appendages to the respective species 

 they fill, or have filled and, with the same principle in view, we 

 take the external impression to be only a part of the matrix 

 (v. Soil, matrix, &c.) 



t It is obvious, that intromission can only take place, in parti- 

 cular bodies ; and that the change, effected by this process, will be 

 more or less perfect, according to the circumstances, under which 

 it is carried on. If, for insiuuce, the original possess parts of such 

 a perishable nature, as to lose their form with the commencement 

 of putrefaction, no mineral representation of those part' will be 

 produced such is the case with the fleshy and succulent ; the 

 I 



