of Cellulose in Starch-grains. 253 



above all be brought forward as a distinctive character; it is, 

 however, not universally valid. Ammoniated oxide of copper 

 dissolves purified cellulose very quickly ; but, so far as my ex- 

 perience goes, it is quite incapable of dissolving a starch-grain, 

 only causing it to swell up. Another solvent for cellulose, which 

 cannot dissolve starch, is the ferment in putrefying potatoes, 

 discovei-ed by Mitscherlich. Nageli thinks the action of this 

 upon cellulose must be attributed to its setting up decomposition 

 in the proteine substances contained in the cell-membranes, 

 and carrying this over to the cellulose, while, as the starch con- 

 tains no proteine, it does not become decomposed. It is pro- 

 bable that this may be the true explanation ; but, before we can 

 admit it as correct, it must be proved by comparative observa- 

 tions on the action of this ferment upon purified cellulose and 

 starch. I have no experience on this point. 



If we agree with Nageli in regarding that portion of the 

 starch-grain insoluble in saliva as cellulose, we may name a 

 number of other substances which dissolve cellulose but not 

 starch-grains. In any case, it is a partial view to deduce the 

 insolubility or the difficult solubility of starch-grains from the 

 insolubility of the substance insoluble in saliva contained in 

 them, since, on the other hand, this latter substance in a puri- 

 fied condition is very readily dissolved by many materials, while 

 in the starch-grain it is protected from their solvent action by 

 its combination with starch. 



From what is above related, I find it impossible to admit that 

 Nageli has conceived the distinctions between cellulose and 

 starch according to nature ; still less am I convinced that he has 

 arrived at proof of the view that the substance left of the starch- 

 grains after the removal of the soluble part by saliva is identical 

 with cellulose. The following facts will show that this substance 

 behaves differently, with a number of reagents, from purified 

 cellulose. 



The grounds upon which Nageli here rests lie especially in 

 the reaction of this substance with iodine (p. 186), its assuming 

 a copper-red or red-brown colour with aqueous solution of iodine, 

 tincture of iodine, or iodide of zinc, and a blue colour when 

 dried up with tincture of iodine and wetted with water, or treated 

 with iodine and sulphuric acid. 



The characters certainly indicate a great similarity to cellulose. 

 I may mention, as a further agreement, that ammoniated oxide 

 of copper dissolves both substances. But let us look at the 

 differences. 



In regard to physical properties, it must be observed that the 

 substance of starch-grains is very brittle, while pure cellulose is 

 perceptibly tough ; further, that, as above-stated, the two sub- 

 stances act in opposite ways on polarized light. 



