CHEMICAL BASIS OF THE ANIMAL BODY. 79 



composition which lie within somewhat similar limits to those already 

 assigned (p. 5) to the proteids. A comparison of these seems to 

 justify the statement that on the whole the mucins contain slightly 

 less carbon and distinctly less nitrogen than do the proteids 1 . 



During his researches on mucin Landwehr 2 obtained a substance to which he 

 gave the name of " animal-gum " from its general similarity to the vegetable products 

 of the same name. He was at first inclined to regard the mucins as mixtures of 

 this carbohydrate with other proteid substances, but this view he subsequently 

 modified 3 . Further investigation has led him to regard animal-gum as occurring in 

 many tissues of the body and to speculate on its physiological and pathological 

 significance 4 . Its isolation from the several tissues is somewhat lengthy and 

 complicated, and for this Landwehr's original papers must be consulted. It 

 dissolves in water to form a readily foaming solution, from which it may be 

 precipitated by alcohol. In alkaline solution it readily dissolves cupric oxide 

 which is not reduced on boiling : when boiled with dilute mineral acids it 

 yields a reducing sugar, but it is not altered by digestion with saliva or pancreatic 

 juice (see also below under carbohydrates). 



It has been already stated that purified mucin (except of bile) yields a carbo- 

 hydrate when heated with acids or stronger alkalis, and a considerable controversy 

 has been carried on as to whether animal-gum is a carbohydrate which occurs in the 

 tissues as a mere companion of the mucins or whether it is in all cases a product of their 

 decomposition. The evidence at hand on this point is not conclusive, and for the 

 present it may be said that, while mucin is often accompanied by animal-gum, the 

 latter has by no means been proved to take its origin from the former. The whole 

 subject requires further investigation. 



Gelatin or Glutin 5 . 



The ultimate fibrils of connective tissue and the organic matter 

 of which bones are largely composed consist of a substance named 

 in the first case ' collagen,' in the second ' ossein.' They are obtained 

 either by digesting carefully cleansed tendons with trypsin, which 

 dissolves up all the tissue-elements except the true collagenous (gela- 

 tiniferous) fibrils 6 , or by extracting bones with dilute acids in the 

 cold, by means of which the inorganic salts are dissolved and the ossein 

 remains as a swollen elastic mass which retains the shape of the 

 original bone. As thus prepared they are insoluble in water, saline 

 solutions and either cold dilute acids or alkalis ; in the former however 

 (acids) they swell up to a transparent gelatinous mass. When subjected 



1 See Liebermann, Biol. Centralb. Bd. vn. (1887-88), S. 60. 



2 Zt. f. physiol. Chem. Bd. vi. (1881), S. 75; vra. (1883), S. 122. 



3 Ibid. Bd. ix. S. 367. 



4 Centralb. f. d. med. Wiss. (1885), S. 369. Pfluger's Arch. Bde. xxxix. (1886), S. 

 193; XL. S. 21. 



5 Glutin must not be confounded with the vegetable proteid ' gluten.' 



6 Kiihne u. Ewald, Verhand. d. naturhist.-med. Ver. Heidelb. Bd. i. N.F. (1877), 

 S. 3. See also Etzinger, Zt. f. Biol. Bd. x. (1874), S. 84. Ewald, Ibid. Bd. xxvi. 

 (1889), S. 1. 



