STRUCTURE.] BEHAVIOUR WITH SULPHURIC ACID. 115 



sometimes white, at other times black, sometimes close 

 together, at other times farther apart, which are at first circular, 

 but become more and more elliptical as they inclose the 

 kernel in their foci. The substance seen between these lines 

 appears sometimes clear, at others dark. Single spots 

 are often remarkably transparent, and a practised micro- 

 scopical observer immediately recognises layers of various 

 thicknesses, the outer ones being thicker than the inner, 

 which, in fresh starch, often appear quite gelatinous. The 

 dark lines never cut the line of the outer envelope, and, how- 

 ever close they are placed to each other at the narrow end, 

 each line always runs round into itself. If a starch grain 

 with distinct black lines is placed under a microscope, it will 

 be seen that the lines, in whatever way they are viewed, 

 always have the same direction. It therefore follows that 

 these are not superficial markings, but are real layers, forming 

 egg-shaped shells packed one over the other, and constituting 

 the entire starch grain. 



It sometimes happens that if a potato full of starch is 

 sliced with a sharp knife, so that the grains of starch are cut 

 through, the inner sections are full of water and more 

 gelatinous than the outer, which are drier and more com- 

 pact. Perfectly dry grains show a smaller number of lines, 

 which, however, are often more distinct, and a broad black 

 line resembling a small layer of air is observable. If the 

 starch is allowed to remain in a solution of gum for a long 

 time, the lines become less and less distinct. If it is dried 

 with the gum, until it forms a tough mass which can be cut 

 with a knife, a great number of sections can be obtained. In 

 these a tolerably homogeneous substance can be seen, which 

 has rather an irregular hole in its centre, arising from the 

 contraction of the moist inner layer. 



If starch is treated with sulphuric acid, under a microscope, 

 various appearances are observed, sooner or later, according 

 as the acid is stronger or weaker. After being for a short 

 time in contact with a strong acid, that point of the grain 

 which is touched by the acid swells into a cloudy mass and 

 gradually dissolves. Grains of starch can often be seen, one 

 of whose ends is dissolved, while the other is well defined and 



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