STRUCTURE AND OFFICES OP STARCH. 211 



sweet juice, which is pressed out from the stems by passing them 

 between rollers. This juice is boiled down into a thick syrup, 

 which crystallises, and deposits the sugar it contains. This is what 

 is commonly known as brown sugar ; and it has to undergo a 

 subsequent process of refining, in order to convert it into white. 

 In Canada and other parts of North America, a good sugar is 

 produced from the Maple, by tapping the - stem when the- sap 

 begins to arise in the spring ; the quantity of sugar obtained, by 

 boiling the sap that flows from one tree during a period of six 

 weeks, is sometimes as much as 30 Ibs. 



335. It is not unfrequently necessary, that a store of nu- 

 tritive matter, which may be required at some future time, 

 should be provided in the Vegetable system ; in such a situation, 

 that it shall be out of the general current of the circulation, and 

 at the same time easily brought into it. In Animals, the fat 

 constitutes a store of this kind. The superfluous nutriment 

 introduced into their system is converted into this substance ; 

 which, besides other purposes that it serves, is ready for the 

 support of the body, when from any cause there is a failure 

 of the supply, on which the animal usually depends. In some 

 animals, this production of fat takes place at regular periods ; 

 thus Bears, which pass nearly the whole winter in sleep, and 

 take little food during that season, become very plump in the 

 autumn, and are observed to be very lean soon after they have 

 emerged from their winter retreat. 



336. Now the Starch, which is found so abundantly in many 

 Plants, and in some part of almost every one, serves the same 

 purpose as fat. It is a gum, slightly altered, and inclosed, as it 

 were, in a series of minute bags, which fill the cells of cellular 

 tissue, and receive the form of these. Starch, when removed 

 from the plant, exists in the form of minute granules ; each of 

 which, when examined with the microscope, is found to consist 

 of a series of layers of a half-fluid substance, the interior ones 

 being nearly fluid like dissolved gum, and those on the outside 

 being almost as firm as membrane. When put into cold water, 

 they retain their structure, as the outside layer is not acted on 

 by that fluid ; but when exposed to a heat of about 160, this 



