278 M. Martin on the Amylum Grains of the Potatoe. 



oblique or side light is obtained — an arrangement whicb cannot 

 be too strongly recommended to microscopists. Before Plossl 

 made this improvement, I had to adopt a substitute, with which 

 every expert observer is probably familiar, but to which it may 

 be as well to call attention, because the success of experiments 

 requiring such nicety greatly depends on the proper adjustment 

 of the light. 



For observations by day-light, the reflector ought to be so 

 adjusted that the greatest quantity of light possible will be, thrown 

 on the stage of the microscope, and the light is to be broken in 

 the following manner. A strip of black paper, 3 inches long 

 and 1 inch wide (*'. e. according to the diameter of the reflector), 

 must be placed, the black side outwards, in such a way over the 

 reflector that a segment on both sides of the latter will remain 

 uncovered, and the light be thrown obliquely on the stage. It will 

 often be expedient to cover the entire half of the reflector, leaving 

 one-half only exposed. I prefer these two methods of adjusting 

 the light to the ordinary diaphragm, because in addition to mo- 

 difying the light, they possess the advantage of producing an 

 obliquely-directed light. 



When the observations are made by candle-light, the following 

 method is to be adopted. A stearine candle, in a candlestick 

 12 inches high, is to be placed at a distance of 12 inches from 

 the microscope, and the object placed in the full light of the 

 reflector. Then placing the fore-finger on the vertically move- 

 able hoop of the reflector, the latter is to be turned a little to 

 the right or left, which will instantaneously alter the light ; ele- 

 vations will cast shadows, cavities will be shaded, and the amy- 

 lum grains will appear as complete bodies to the eye of the ob- 

 server. I would advise that all observations be conducted both 

 by candle-light (not by lamp-light, which may be too glaring) 

 and day-light, because a comparison of the different results serves 

 as a check to erroneous conclusions. 



2. Passing over the facts, more or less known, concerning the 

 external appearance of the amylum grains of the potatoe, and 

 also the experiments upon the kernel, the layers, the action of 

 acids, alkalies, roasting, &c., I at once proceed to the peculiari- 

 ties which appear on boiling the amylum. These phpenomena, 

 which are of a highly interesting character, are difficult to ob- 

 serve, and not yet thoroughly understood. The probable cause 

 of their not having been more diligently studied and more 

 thoroughly investigated is, that most microscopists, Fritsche 

 among the mmiber, commence the process by means of a current 

 of heated air from a candle or lamp, and only begin to observe 

 the phenomena when they have nearly terminated. 



I have succeeded in inventing a method by which the boiling 



