M. Martin on the Amylum Grains of the Potatoe. 279 



can be conducted under the microscope without endangering it, 

 and the effect on one and the same grain be observed from the 

 first to the last stage. I have thus been enabled to establish the 

 following facts, which will, I trust, correct the present views on 

 the structure of the amylum grains of the potatoe. 



The method I employed in prosecuting these experiments is 

 as follows : — 



Between two very thin glasses of the same size as the stage of 

 the microscope, a little amylum with a sufficient quantity of 

 water is to be put, and the former well spread out with the finger 

 to prevent as much as possible the formation of bubbles. The 

 number of amylum grains in the field of view should not exceed 

 ten or fifteen. The glasses should lie freely on the spring-piece, 

 which must be raised by means of two pieces of cork or thick 

 coins introduced below it ; so that while the two glasses are 

 lying right upon the object-bearer, a current of cold air will 

 ascend from below, to permit the little flame to continue burn- 

 ing in the hole of or below the stage. As the glasses are wide, 

 they protect the microscope from too great a heat or other 

 danger. The small flame is to be obtained from a common 

 thread, doubled and slightly waxed. This, when ignited, gives a 

 flame quite sufficient to boil the amylum. This method of ap- 

 plying heat is adapted to other experiments, and appears far 

 preferable to the usual one of heating the extreme end of the 

 glass on which the object is placed, until the heat is conducted 

 to the object itself. 



An assistant can hold the flame to the glasses by inserting it 

 from below into the hole of the stage, and withdraw it if any 

 alteration be observed until the paste is formed, or more correctly 

 speaking, until the amylum grains swell up and are completely 

 unfolded. But it will be much better if the observer apply the 

 flame himself, in which case it may perhaps be sometimes extin- 

 guished, yet a little practice will soon give dexterity in the ope- 

 ration. The best way is to hold the thread, which being stiff 

 will remain upright, between the thumb and fore-finger, and to 

 rest the little finger on the table supporting the microscope. 

 Tliis will steady the hand, and the flame can be constantly kept 

 under the centre of the stage. If the heat be unintermitting, 

 the operation, especially in its last stage, proceeds very rapidly, 

 and it will be necessary to repeat the experiment twenty or thirty 

 times IkI'i .re the mind can clearly comprehend the entire process. 

 It is best to employ middle-sized grains at first, and afterwards 

 large onea only. 



3. According to my observations, the phsenomena which take 

 place during the process of boiling are as follows:- — First, the 

 amylum grain sinks in, in that place where, according to I'Yitsche, 



