COMPOUND P ROTE IDS. 61 
crusocreatinine, C 5 H 8 N 4 0, and amphicreatinine, C,,II u ,X 7 0.,). These leuco- 
mainesare regarded by Gautier, Bouchard, Pouchet, and others, 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 Bubstances 
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 
ylobin and its compounds, chlorocruorin 2 (found in the blood 
of certain worms), and hceinocyanin 3 (found in the blood of many 
molluscs and Crustacea). Haemoglobin and chlorocruorin are compounds 
of proteids, with an iron-containing pigment. Hiemocyanin 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 Haemoglobin with its derivatives and allies will be 
considered in a separate article. 
2. Ghtco- proteids. — Compounds of proteids with members of the 
carbohydrate group. This class includes mucins, mucoids, hyalogens 
and phospho-gluco-proteids. 
3. Nuclein. — Compounds of proteid with phosphoric acid, or with 
nucleic acid. 
4. Nucleo-proteids. — Compounds of proteid with nuclein. 
5. Lecith-afbumins. — 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 Fehling'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. f. physiol. Chem., Strassburg, Bd. xiii. S. 562 ; Stadthagen and Brieger, 
Virchow's Archie, Bd. cxv.; Stadthagen, Ztschr. f. klin. Med., Berlin, 1889, Bd. xv. Hefte 
5 and 6 ; Pouchet, Compt. rend. Acad. d. sc, Paris, tome xcviii. p. 1360 ; Bouchard, ibid., 
tome cii. pp. 669, 727, 1127 ; Griffiths, ibid., tomes cxiii., cxiv., and cxv. ; Gautier, Bull. 
Acad, de med., Paris, 1886, tome xix. A very complete bibliography will be found in 
Huppert-Neubauer's "Analyse des Haras," 9th edition, p. 241. 
2 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, Ser. 2, tome xlvi. K"o. 
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. Boy. Soc. London, 
1896, vol. lix. p. 339. 
