MELANIN COLOR FORMATION. 325 



the possibility of accounting for them on the basis of specific, 

 independent transmissions, once for all segregated by the germ 

 cells. 



Rather fortunately for the completer view of our present 

 theme, pathologists and clinicians have been frequently confronted 

 with cases of incomplete tyrosin oxidation (alkaptonuria), and 

 unusual and pathological melanin pigmentations (melanotic 

 tumors, Addison's disease, ochronosis) in the human body. 

 These subjects because of their medical bearings have received 

 a very great amount of attention, of accurate and searching study, 

 at the hands of investigators. It seems self-evident that the 

 student of melanogenesis should here find much data to interest 

 him. 



In the condition known as " alkaptonuria " l the alkapton acids 

 uroleuic and homogentisic appear in the urine. The last- 

 named compound represents a stage in the oxidation of tyrosin. 

 The intermediate stages and the chemical structure of these sev- 

 eral compounds may be best understood by reference to Table II. 

 Our interest in these early stages of tyrosin oxidation is very 

 great since we know that the same, or similar steps, lead in special 

 cases to the formation of melanin. 2 Neubauer ('08) has very 

 recently determined the exact course of the first four steps of 

 tyrosin oxidation as they occur in the living (human) body. The 

 chemical expression of these stages is given in the table. 



Garrod ('02) found that certain individuals, who in their youth 

 excreted urine containing homogentisic and urolencic 3 acids, 

 produced only the former during adult life. Other cases of tem- 

 porary and intermittent alkaptonuria are known. Here certainly 

 the evidence of our senses is simply that the pow er of the organ- 

 ism to oxidise tyrosin compounds is not dependent primarily upon 

 germinal segregations, but rather upon tissue activities, relations 



Resume and literature by Falta, Biochem. Centralb., 3, p. 174, 1904. See also 

 Abderhalden, " Lehrbuch der Physioiogischen Chemie," Berlin, 1906, pp. 294-298; 

 and Neubauer ('08), loc. cit. 



2 A chemical research directed to the determination of the reasons for some tyrosin 

 oxidation leading to melanin formation, instead of to the usual end-products of oxida- 

 tion NH 3 , CO 2 , H 2 O, etc., would be of the greatest interest and help in studies on 

 the physiology, development and heredity of color. 



3 According to Neubauer ('08) this body is not an intermediate step in the oxi- 

 dation of tyrosin to homogentisic acid. 



