298 DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



to determine the beginning of disorganization of the grain by heat, since with the very 

 onset of gelatinization the polariscopical properties begin to disappear. In tliese exami- 

 nations (excepting in determining the temperature of gelatinization) the grains were 

 mounted in Canada balsam. The general characteristics, distinctness, shape, regularity, 

 and position of the interference figure, and also the approximate degree of anisotropy or 

 intensity of polarization were readily studied. By the aid of selenite it was determined 

 whether the optical properties were negative or positive, and also the size, shape, anil 

 regularity of the quadrants, as well as the intensity and pureness of the blue and yellow 

 colors. In spherical grains with centrally located hila, the two parts of the "cross" inter- 

 sect at the hUum, or mathematical center, of the grain, so that the term quadrant has a 

 proper application; but in the case of grains having eccentric hila the position of the point 

 of intersection of the two parts of the cross, together with their curvatures, may destroy 

 every semblance of quadrants according to the conventional definition of this word. This 

 term has therefore been used in a very broad sense throughout our investigation to indi- 

 cate the four parts of the grain that are defined by the two parts of the cross, in preference 

 to the great multipUcity of terms that would be required to define these parts if great 

 accuracy were attempted. Likewise, for convenience we have referred to the "lines" 

 of the interference figure in preference to the "arms" of the cross. 



All starches are "optically negative," hence no special references have been made in 

 the text in this particular. 



TEMPERATURE OF GELATINIZATION. 



While the records of various investigators indicate that there are more or less marked 

 differences in the temperatures of gelatinization of different kinds of starches, and even 

 in case of different gi'ains of the same starch, the figures appljang to the same kind of starch 

 are generally so at variance that not much value is to be attached to them. The sources 

 of fallacy in such observations, unless the determinations are made with the greatest 

 precautions, are well known to every biochemist. We therefore carried out this work 

 with especial care. A long quadrangular water-bath was used, holding about 4 liters of 

 water; one end was placed over the gas flame, and in the other end was inserted a ther- 

 mometer which was calibrated in tenths centigrade, but which could readily be read in 

 hundredths. A small quantity of starch with 10 c.c. of water was placed in a test-tube, 

 into which was inserted tlu-ough a perforated cork a thermometer similar to the one in 

 the water-bath, and the test-tube inunersed in a suspended wire basket in the part of the 

 water-bath farthest from the flame. The temperature of the water was raised very slowly, 

 and the water occasionally stuTed, so that at no time did the two thermometers differ 

 more than about 2. As the temperature increased, specimens of the starch were ex- 

 amined at intervals, the tube being shaken, and a specimen being obtained by inserting 

 the end of the pipette to the bottom of the tube, a fresh pipette being used to remove each 

 specimen. Each specimen was placed on a slide, upon which was recorded both tempera- 

 tures, and the slide was examined in the polarizing microscope. The temperature at which 

 there is a disappearance of anisotropy of practically all of the grains was recorded as the 

 temperature of the tube. The lower temperature recorded on the slide was that of the 

 thermometer in the test-tube, and the higher temperature that of the water-bath. The 

 actual temperature of gelatinization lies somewhere between the two, and for convenience, 

 especially for purposes of comparison, the mean of the two was for obvious means taken 

 as the "temperature of gelatinization." In the records in Part II all tlu-ee temperatures 

 are given in accordance with the foregoing. 



ACTIONS OF SWELLING REAGENTS. 

 Quite a number of swelling or gelatinizing reagents, of very diverse chemical com- 

 position and exhibiting more or less individuality of action, have been used by various 



