282 HISTOLOGY OF THE MORBID PROCESSES. 



by aqueous solutions of iodine, while the normal tissues acquire a 

 yellow color. Under the microscope the brown color has a marked 

 reddish tinge. Solutions of methyl-violet give amyloid a red color 

 and stain the rest of the tissues blue or bluish-violet. It is upon 

 these reactions, and not upon the optical appearance of the material 

 when unstained, that the recognition of amyloid depends. 



Its most frequent situation is in the walls of the smaller blood- 

 vessels, where it lies in the deeper layers of the intima or in the 

 muscular coat. It may also be deposited around the endothelial 

 walls of the capillaries (Fig. 253). 



Amyloid infiltration occurs in syphilis, advanced tuberculosis 

 (especially of bone), long-continued suppuration, and similar condi- 

 tions in which there is profound cachexia. It evidently depends 

 upon conditions of marked malnutrition or chronic toxic conditions, 

 and it is believed that its occurrence depends upon the inability of 

 the tissue-cells to utilize the proteids that are present in the inter- 

 stitial serum. These are thought to accumulate and gradually be- 

 come transformed into amyloid. The deposition of amyloid, accord- 

 ing to this hypothesis, would depend primarily upon a lack of power 

 to assimilate proteids on the part of the cells. 



The presence of amyloid between the cellular elements of the 

 tissue interferes with their nutrition, and they suifer atrophy. 



11. Calcareous Infiltration (Figs. 254 and 255). There appears to 

 be a marked affinity between necrosed tissues, or tissues of low vital- 

 ity, and the salts of lime that are found in the circulating fluids of 

 the body, which leads to a deposit of the latter within those tis- 

 sues. The cheesy material that results from tubercular or other proc- 

 esses is prone to this form of infiltration. Cicatricial tissue, when 

 abundant and poorly nourished, may also be the seat of lime-deposits. 

 Similar deposits are sometimes associated with those of urates in the 

 inflammatory nodules of low vitality that characterize gout. Bits 

 of organic or other foreign matter that are exposed to fluids contain- 

 ing salts of lime are liable to become encrusted with a coating of cal- 

 careous material. This is the origin of many renal and other calculi 

 and of the vein-stones that form around small thrombi of occasional 

 occurrence where the circulation is very sluggish ; e. g., in the 

 venous plexuses within the pelvis, or behind the valves that occur 

 in the course of most of the veins. Calcification of cartilage is also 

 common after the individual has attained a certain age. Tumors 

 in which the tissues are of low vitality or have degenerated are 



