354 Ndgelfs theory of molecular structure [BOOK n. 



starch-grain very poor in substance, but showing exactly the 

 original stratification and giving no blue colour with iodine ; 

 this Nageli named starch-cellulose. It followed from this 

 behaviour, that two chemically different molecules lie every- 

 where side by side in the grain of starch, much as if red and 

 yellow bricks had been so employed to build a house, that 

 when all the yellow bricks were afterwards removed, the red 

 alone would still represent the wall in its original form as a 

 whole though in a looser condition. He arrived at similar 

 results in the case of the crystalloid proteid bodies, which 

 Theodor Hartig discovered, and Radlkofer had examined 

 crystallographically, Maschke chemically. Since it is possible 

 in the same manner to extract the so-called incrusting matters 

 from cell-membranes without essentially altering their form, 

 and to obtain ash-skeletons of them which imitate all the 

 delicacies of their structure, the comparison adopted above 

 may also be applied in still more complex manner to the 

 molecular structure of these membranes ; and indeed many 

 considerations lead to the belief, that the ideas which Nageli 

 obtained from starch-grains may be applied with some modifica- 

 tions to the structure of protoplasm also. 



We said that the appearances in the starch-grains led Nageli 

 to suppose that their molecules are not spherical but poly- 

 hedral, and the question naturally arose whether they are 

 really crystalline. The point could be settled by the use of 

 polarised light, to which different observers had already turned 

 their attention. Erlach in 1847, Ehrenberg in 1849, had em- 

 ployed polarised light for the determination of microscopic 

 objects, without however arriving at any conclusions on the 

 subject of molecular structure ; Schacht indeed at a later time 

 declared such observations to be a pretty amusement, but 

 without scientific value. But soon we have once more one of 

 von Mohl's careful and solid investigations ('Botanische Zeitung,' 

 1858), in which with the aid of technical improvements in 

 the apparatus he arrived at conclusions respecting the nature 



