SECRETION. 99 



ble quantity, and forms the Sago, Arrowroot, Cassava 

 Tapioca, and Salop, etc., etc., of commerce. 



107. In the tubers of the Orchises, and other plants 

 when examined by the microscope, the Fecula may be 

 seen as minute globules ; these globules of amylaceous 

 matter when placed in water, of 112 expand, but the 

 temperature of 212 causes the bladders to burst, when, 

 that which was contained within them is deposited in the 

 water, whilst the rest is precipitated : that contained in 

 solution is the Dextrine of Biot. If the solution is filtered 

 and Iodine added to it, a yellowish brown colour is pro- 

 duced, but if added to the precipitate a blue or violet 

 colour appears ; showing therefore that the grains of 

 Fecula are composed of different substances, and that 

 as a test of starch, Iodine acts upon the coats or exter- 

 nal portions of the grains, with which it only produces a 

 blue colour. 



108. A principle termed Diatase also exists in starch, 

 the action of which upon fresh Fecula is peculiar. Ac- 

 cording to Guerrin, if 100 parts of starch are dissolved 

 in 1393 of water, and mixed with only a little more 

 than twelve parts of Diatase, and subjected to a tem- 

 perature of 68 Fah., 77.64 parts of sugar are obtained, 

 whilst upon a great number of other vegetable substances 

 Diatase it has no action at all. 



109. The characters which mark the nature of amy- 

 laceous matter are thus summed up by Pay en. A com- 

 plete insolubility in water and alcohol, both directly and 

 at low temperature, a great extensibility, and a remark- 

 able contractility under the influence of several agents, 

 a blue or slightly violet colour, when acted upon by 

 the solution of Iodine, the augmentation and predo- 

 minance of the colour red in this combination, and its 

 great instability during the progress of the disaggrega- 

 tion of the grains of Fecula, and at last a complete 

 cessation of all colourability by means of Iodine as 

 soon as the disaggregation is carried to the point repre- 

 senting its maximum of solubility during cold, that is 

 to say, its complete transition to the state of Dextrine. 



