98 Mr W. Gardiner, On the constitution [Feb. 11, 



the question the difficulties connected with the mere analysis of 

 these organic compounds ; any one at all acquainted with chemical 

 methods, will at once understand how hard it is to deal with even 

 the ordinary manipulative details of such colloidal bodies as 

 mucilages, where even the washing, and filtration, offer almost 

 insuperable obstacles to the obtaining of a pure product. 



We will first consider the gums and the pectous substances. 

 Chemists have taught us that the gums, as represented for 

 instance by gum-arabic, usually consist of the potassium and 

 calcium salts of a weak acid : arabic acid or arabin. By the action 

 of dilute acids upon the body; metarabic acid, and finally a 

 glucose (arabinose) is formed 1 . Another variety was described by 

 Heichardt 2 which is distinguished in that it does not give arabinose 

 as a result of the acid of an acid. 



From the mucilage occurring in the pulp of fruit, a substance — 

 pectose — has been extracted, which by the action of acids gives 

 soluble pectin, and further by the action of the peculiar pectose 

 ferment described by Fre'my, or simply by a regulated treatment 

 with dilute alkalies and acids, gives rise to pectic, parapectic and 

 finally metapectic acid. 



The remarkable similarity between the properties of Arabic 

 acid on the one hand, and Pectic on the other, appear to point to 

 the probability, that the two bodies are identical, and in the 

 opinion of Reichardt and Dragendorff and (since he puts all the 

 gums and mucilages under the head of Pectose) of Fre'my, the 

 pectin substances may in fact be regarded simply as varieties of 

 the mucilages and gums. Of the mucilages in particular, the 

 varieties appear to be very numerous, for in addition to Berg's 

 discovery of Lichenin which I have already mentioned, Kirchner 3 

 believes he has obtained a pure mucilage from Quince seeds, and 

 Thomsen 4 from ligneous tissue has extracted a wood-gum. Gelose 5 

 which is related to Lichenin, has been found to occur in many 

 algae, and more recently from Fucus Amylaceus has been separated 

 a substance which though allied to Gelose and Lichenin differs 

 markedly from them both 6 . 



From a 'priori considerations, it does not seem improbable that 

 certain kinds of mucilage may be regarded as formed from the 

 cellulose in consequence of excessive hydration ; but since, as 



1 According to Scheibler, Ber. d. d. chem. Ges. vi. 620, two sugars (one crystal- 

 lisable and the other uncrystallisable) and an acid whose barium salt is insoluble 

 in alcohol, are produced. 



2 Eeichardt, Ber. d. d. chem. Ges. vm. 807, 1875. 



3 Kirchner, Ueber Pflanzenschleim. Diss. Inaug. Gottingen, 1874. 



4 Thomsen, Journ. Bract. Chem. (2) xix. 146, 1879. 



5 Morin and Porumbaru, Comptes rendus, xc. 924, 1081, 1810. 



6 Sitzber. Naturfors. Ges. Dorpat, vi. p. 39, 1881, 



