So? 



fl-ystalline mass, which in fact sometimes colours red with iodine, 

 is washed out with much water, the dextrine, and with it the 

 "anijiodextrine reaction " quite disappears, lo make place for 

 pure blue. 



The crystals may also be obtained from solulile |)Otato starch. 

 Such starch is prepared by keeping raw starch during 10 days under 

 10 7o-ic cold h3'drochloric acid. 



Crystal discs (bolidiscs) result very easily from wheat starch. 

 The heating must be somewhat longer and the temperature higher 

 than for potato starch. Besides, it is more difficult to obtain a per- 

 fectly clear solution from wheat paste. 



Fig. 3 shows, 230 times magnified, the discs formed in a beaker- 

 glass of 100 cm', in which wheat starch, previously boiled in distilled 

 water, is heated to 160° C. The discs are thinnest in the middle 

 and from this centre tlie needles radiate. The discs resemble natural 

 wheat starch as well in shape as in size. With polarised light I could 

 not, however, perceive anything of the axial cross, which is so very 

 obvious in natural starch. 1 suppose that it does exist, but is too 

 feeble to be ül)served. It is, namely, a fact that the structure of 

 the spherites and discs is much looser than that of natural starch, 

 so that in a volume unit of the latter many more needles occur 

 tiian in the discs and spherites. If now the double refraction of the 

 separate needles be not great, their united power in the discs need 

 not necessarily show the same as is seen in the natural grains. 



That the double refraction of the common starch grains reposes 

 on their crystalline nature and not on tangential and radial tensions, 

 may be concluded from the fact, that the axial cross is in the usual 

 way perceptible in soluble starch. As this substance is prepared with 

 strong hydi-ochloric acid, whereby from 10 to IB 7o of the dry 

 substance is extracted, it must be conchided that all tensions, originally 

 present in the grain, disappear. 



That the discs may also be obtained from potato starch is demon- 

 strated in Fig. 3, where lO'/o potato starch, after boiling and gela- 

 tinising in distilled water, in a 100 cm' beakerglass, heated to 125° C 

 during S'/, hour, and after 24 hours of crystallisation in a room of 

 about 16° C, is figured 600 times magnified. 



Bv moving the coverglass on the slide, many discs ma}* be 

 observed laterally, as is clearly seen in the photo. In the preparation 

 of wheat starch used for fig. 3, all the grains are lying on their 

 broad side. 



The crystal discs of the starch are now and then referred to in 

 literature as "Jacquelain discs", but without any allusion to their 



