158 FOODS AND FOOD ADULTERANTS. 



copal varnish thinned with turpentine and introducing the starch and 

 glycerine mixture, fixing the cover glass ou after running some of the 

 cement over the top of the ring. A little experience will enable one to 

 put the right amount of liquid in the cell and to make a preparation 

 which will keep for some time. After several months, however, it is 

 difficult to distinguish the rings which mark the development of the 

 granule, and although for reference as to size and form the preparation 

 is satisfactory, it is always advisable in doubtful cases to examine some 

 fresh material. 



For other purposes the starches should be mounted in prepared Can- 

 ada balsam or dammar by well-known methods. In this medium they 

 can be preserved indefinitely, but are scarcely visible with ordinary 

 illumination, and must be viewed by polarized light, which brings out 

 distinctive characters, not seen as well or at all in other mounts. 



Appearance in glycerine and water. When mounted in the manner 

 already described, or in water alone if for only temporary use, and ex- 

 amined under a microscope with an objective of equivalent focus of 

 one-half to one-fifth inch, and with means for oblique illumination, the 

 starches will display the characteristics which have been mentioned, 

 and which are illustrated on Plates 26, 27, and 28. These illustrations 

 have been drawn from nature by Dr. George Marx, and represent the 

 starches as nearly as possible, as they are seen, and not as in many of 

 the absurd illustrations of the handbooks of rnicroscopists of the past 

 and present day, which are entirely ideal, representing the granules 

 not as extremely translucent bodies, but with the rings or layers as 

 strongly-marked lines. Examined in this manner the size, shape, pres- 

 ence or absence of a nucleus or hiluin, and of the rings and their ar- 

 rangement, can be made out, and the starch referred to its proper posi- 

 tion. 



Appearance in balsam with polarized light. Mounted in balsam the 

 starches are scarcely visible under any form of illumination with ordi- 

 nary light, the index of refraction of the granules and the balsam being 

 so nearly alike. When, however, polarized light is used the effect is a 

 striking one, and is illustrated in Plates 19 to 21. It is very easy to 

 distinguish all the characteristics, except the rings, the center of the 

 cross being at the nucleus of the granule. 



With the selenite plate a play of colors is produced, which is peculiar 

 to some of the starches and forms the basis of Blyth's classification. 



The principal starches which are met with may be described as fol- 

 lows, in connection with our illustrations, beginning with those of the 

 arrowroot class, including the potato, ginger, and turmeric. 



Potato starch. The starch grains of the potato are very variable in 

 size, being found from .05 to .10 mm in length, and in shape from oval and 

 allied forms to irregular and even round in the smallest. These varia- 

 tions are illustrated in Fig. 57, but the frequency of the smaller granules 

 is not as evident as in Figs. 30 and 31. The layers are visible in some 

 granules with great distinctness and in others hardly at all, being rather 



