56 PIGMENTATION. 



bones, where they are, so to say, inlaid near the ossifying border 

 of the cartilage. 



So much for the histological details of calcification as it 

 occurs in cartilage. Its individual features recur in the most 

 various tissues. In order not to anticipate the special descrip- 

 tions contained in the second part of the present work, we must 

 content ourselves here with the remark that calcification, where- 

 ever it occurs, is always a true infiltration. The specific form of 

 the infiltrated structures, at least in its coarser outlines, is never 

 effaced. We are able, as a rule, to restore matters to their 

 previous condition by simply removing the earthy salts with 

 hydrochloric acid. 



c. Pigmentation. 



§ 55. Pigmentation (chromatosis) is one of the most interest- 

 in o- subjects in pathological histology. Its limits are not very 

 well defined.* I must premise therefore, that I do not intend, 

 under the head of Pigmentation, to discuss every change of 

 colom' which may occasionally be exhibited by diseased parts, but 

 to confine my attention to those positive colorations which are 

 due to the infiltration of some pigmentary substance into the 

 tissues. Eed, yellow, brown, and black pigmentary particles, with 

 every imaginable intermediate tint, may be met with as infiltra- 

 tions. They are all, however, ultimately derived from one and 

 the same source — the hsematin of the red blood-corpuscles. 



We are not fully acquainted with the chemical composition 

 of hsematin ; we do not know how it is produced. Itself, in all 

 probability, an albuminous body, it is intimately combined in 

 the red corpuscles Avith another albuminous substance which is 

 destitute of colour {glohdin). This compound, under certain 

 conditions, crystallises in long red needles {hwmato-crystallin). 

 To understand how yellow, brown, and black pigments may be 

 derived from the colouring-matter of the blood, we must first 

 glance at the physiological metamorphoses to which this substance 



* For example, all those tissue-changes -which have already been 

 described, cause some peculiar coloration or decolorisation of the affected 

 structures. So too, desiccation, shrivelling, condensation may all modify 

 the refractive index, and so alter the optical properties of the tissues. 



