24'2 11. von Mohl on the supposed Existence 



l)y macerating the starch-grains, at a moderate heat (about 104P 

 to 120° F.) in solvent fluids, particularly in saliva, which ex- 

 tracted tlie compound which becomes blue with iodine (the 

 proper starch,) and leaves behind the starch-grains essentially 

 unaltered in their anatomical conditions, but with totally different 

 chemical properties. For the compound dissolved out of the 

 starch he proposes the term granulose (p. 209) ; the remaining 

 substance of the grains is described as cellulose*. 



As my critical repetition of Nageli^s observations leads me to 

 regard this last opinion as unfounded, I venture to publish an 

 account of my investigations. 



In making the inquiry, I chiefly employed as material the 

 starch of the rhizome of Canna indica. For the extraction of 

 the substance coloured blue by iodine I used saliva, because 

 this acts more quickly than extract of malt. The attempt to 

 obtain the same result by organic acids, in the manner described 

 (certainly in no great detail) by Melsens, was unsuccessful. It 

 is necessary to discover by experiment, for each kind of starch, 

 the favourable temperature at which it is to be treated ; for at 

 too low a temperature the action does not take place at all, or 

 only very slowly, while too high a temperature produces swelling 

 up and total solution of the granule. In consequence of the latter 

 circumstance, I was less regardful of the maintenance of a con- 

 stant temperature in the hatching- machine in which I heated 

 the grains than that a certain definite degree of heat should not 

 be exceeded. In the starch of Canna, the extraction of the 

 starch-substance began at a temperature of 95°-104°F., and 

 advanced very slowly and regularly from the periphery of the 

 granule towards its centre, unless it could penetrate by an acci- 

 dental crack in the granule, in which case the solution in the 

 interior of the granule proceeded rapidly onward from the sides 

 of the crack. At a temperature of 120°-131° the extraction of 

 the soluble part of the granule was completed in a few hours. 

 A far lower temperature suffices for the extraction of the starch 

 of wheat, while that of potatoes requires a much higher one. If 

 the operation is carried on at a low temperature, the experi- 

 ment lasting then several days, we must not neglect to pour off 



that the layers are formed from without inwards, the older expanding to 

 make room for the new ones. — A. H. 



* As often happens, the same discovery of the composition of the starch- 

 grain was made, apparently independently of Nageli, by Melsens (Institut, 

 1857, p. 161)j who extracted the substance coloured blue by iodine by means 

 of organic acids, diastase, and pepsine, and conjectured that the residue 

 consisted of a nitrogenous substance and another standing near to cellu- 

 lose. I am unaware whether he has made known his researches in greater 

 detail than in the work here cited. 



