466 VICTOR C. MYERS 



practically the same substance. It has become customary to refer to the 

 pigment of both feces and urine as urobilin. Urobilin is generally excreted 

 to a large extent in the form of a chromogen, urobilinogen, which on ex- 

 posure to light is converted to urobilin. Normally a considerable part of 

 the urobilin (ogen) of the intestines is reabsorbed and reconverted to 

 bile pigments. In certain diseases of the liver, the liver cells partially 

 lose this capacity, thus giving rise to an increased excretion of urobilinogen 

 in the urine. Owing to the greatly increased destruction of red cells in 

 pernicious anemia (but not in secondary anemia) the output of urobilin 

 in the stool is greatly increased, an observation which is of considerable 

 value in differentiating the two forms of anemia. 



Human biliary calculi or gallstones are as a rule composed largely of 

 cholesterol in man. Occasionally the stones are pearly white, indicating 

 that they are almost entirely cholesterol, although more often they are 

 somewhat pigmented, sometimes very much so, indicating a mixture with 

 calcium salts of bilirubin and biliverdin. Stones made up largely of 

 pigments are not often found in man. The etiology of gallstone formation 

 is not as yet clear. 



Connective Tissues 



The cellular elements of typical connective tissues and gelatin-yielding 

 fibrils are imbedded in an interstitial or intracellular substance. The 

 fibrils consist of collagen^ while the interstitial substance contains chiefly 

 mucoid, besides small amounts of albumin and globulin. In yellow elastic 

 tissue, fibrils containing elastin are also present. Four types of con- 

 nective tissue will be mentioned, (1) white fibrous tissue, (2) yellow 

 elastic tissue, (3) cartilage and (4) bone. 



The tendo Achillis is generally taken as a typical example of white 

 fibrous tissue. According to the analyses of Buerger and Gies, the 

 tendo Achillis of the ox contains 31.6 per cent of collagen in the fresh 

 tissue and 85 per cent in the dry tissue, together with 4.4 per cent of 

 elastin and 3.5 per cent of mucoid. 



The ligamentum nuchse of the ox is the classic illustration of yellow 

 elastic tissue. Vandegrift and Gies give the content of elastwi in the 

 fresh tissue as 31.7 per cent, and in the dry tissue as 74.6 per cent, together 

 with 17 per cent of collagen and 1.2 per cent of mucoid. 



Cartilage is closely related to white connective tissue, since it con- 

 tains a relatively large amount of collagen. In addition it contains an 

 albuminoid, chondroalbuminoid, and chondroitin-sulphuric acid. Chon- 

 dromucoid differs from the mucoids found in other connective tissues in 

 the large amount of chondroitin-sulphuric acid obtained on decomposition. 

 This acid is also found in bone, ligament and other tissues. Under the 

 action of acid hydrolysis, chondroitin is first formed, then later chondrosin. 



