COMPOUND PROTEIDS. 61 



crusocreatinine, C 5 H 8 N 4 0, and amphicreatinine, C (J H 19 N r 4 ). 

 maines are regarded by Gautier, Bouchard, Pouchet, and others, 



These leuco- 

 , as feebly toxic 



products of metabolism, from which the organism is normally freed by excretion, 

 or by destructive oxidation; it has been suggested that their retention in 

 the body may be the cause of certain obscure pathological conditions. The 

 poisonous properties of normal urine are regarded by some as due to 

 alkaloids of this nature, while others (Stadthagen) look upon the inorganic, 

 especially the potassium, salts of urine, as the toxic agents. 1 



COMPOUND PROTEIDS. 



The compound proteids are compounds of albuminous substances 

 with other materials, which are as a rule also of a complex nature. 

 They may be divided into the following groups : 



1. Respiratory ^ pigments. - - The most important of these are 

 haemoglobin and its compounds, chlorocruorin 2 (found in the blood 

 of certain worms), and hcemocyanin 3 (found in the blood of many 

 molluscs and Crustacea). Haemoglobin and chlorocruorin are compounds 

 of proteids, with an iron-containing pigment. ILemocyanin contains 

 copper in its molecule. Turacin, the red pigment in the feathers of 

 certain birds (plantain-eaters), also contains copper, and though not 

 respiratory in function, should probably be included in the same group 

 of substances. 4 Hemoglobin with its derivatives and allies will be 

 considered in a separate article. 



2. Grluco - proteids. Compounds of proteids with members of the 

 carbohydrate group. This class includes mucins, mucoids, hyalogens 

 and phospho-gluco-proteids. 



3. Nudein. Compounds of proteid with phosphoric acid, or with 

 nucleic acid. 



4. Nudeo-proteids. Compounds of proteid with nuclein. 



5. Lecitli-albumins. Compounds of proteid with lecithin. 

 We may consider the last four groups in detail. 



The gluco - proteids. The gluco -proteids are mostly free from 

 phosphorus (mucins, mucoids, and hyalogens), but some contain phos- 

 phorus (phospho-gluco-proteids). 



Mucins. The mucins are colloid, viscous substances of acid nature, 

 soluble in alkalis, but precipitable from such solution by acetic acid. 

 On boiling with dilute mineral acid they yield a substance which 

 reduces Eehling's solution. They are found in the secretion of mucous 

 glands, including the mucous salivary glands, and of slimy animals like 



1 For the principal papers on alkaloidal substances in urine, see Baumann and 

 Udranszky, Ztschr. /. physiol. Chem., Strassburg, Bd. xiii. S. 562 ; Stadthagen and Brieger, 

 Virchow'* Archiv, Bd. cxv.; Stadthagen, Ztschr. f. Tclin. Mad., Berlin, 1889, Bd. xv. Hefte 

 5 and 6 ; Pouchet, Compt. rend. Acad. d. sc., Pt,ris, tome xcviii. p. 1360 ; Bouchard, ibid., 

 tome cii. pp. 669, 727, 1127 ; Griffiths, ibid., tomes cxiii., cxiv., and cxv. ; Gantier, Bull. 

 Acad. dc med., Paris, 1886, tome xix. A very complete bibliography will be found in 

 Huppert-Neubauer's "Analyse des Harns," 9th edition, p. 241. 



- Quatrefages, see Gamgee, "Physiological Chemistry," vol. i. p. 131; Krukenberg, 

 "Vergl. physiol. Studien," 2te Reihe. Abth. 1, S. 87; Lankester, Journ. Anat. and 

 Physiol., London, vol. ii. p. 114 ; vol. iii. p. 119. ; MacMunn, Quart. Journ. Micr. Sc., 

 London, Oct. 1885. 



3 Fredericq, Bull. Acad. roy. de mid. de Belg., Bruxelles, 1878, Se"r. 2, tome xlvi. Xo. 

 11 ; Halliburton, Journ. Physiol., Cambridge and London, vol. vi. p. 300. In the latter 

 paper numerous references to other writers will be found. 



4 A. H. Church, Proc. Roy. Soc. London, 1869, vol. xvii. p. 436 ; Phil. Trans., London, 

 1869, vol. clix. p. 627 ; 1892, vol. clxxxiii. p. 511 ; A. Gamgee, Proc. Roy. Soc. London, 

 1896, vol. lix. p. 339. 



