Microscopical Anatomij. 67 



dition : yet chemical analysis would reveal the presence of 

 starch and of cellulose, besides certain nitrogenous principles, &c. 

 When the potato is boiled, it becomes more or less crumbling, 

 much of it falls into the ' floury' state. A portion of this ' flour,' 

 placed under the microscope, is found to consist of minute 

 roundish or oval bags, of a delicate membrane, which have be- 

 come more or less separated by boiling. They may be obtained 

 in a still better condition for examuiation by soaking a fragment 

 of potato for several days in water, until it appears softened and 

 almost liquefied. These little sacs or bags are formed of the cel- 

 lulose, and contain the starch and the nitrogenous principles. 

 If we tear these sacs or crush them down, they lose their dis- 

 tinctive character as constituents of the particular structure of 

 the potato-tuber, and become mere fragments of cellulose, recog- 

 nizable as such by chemical tests, and ther.'by known to be 

 of organic origin, but deprived of all the characteristic pecu- 

 liarities as constituent parts of a particular organization. 



All animal and vegetable organs are composed of microscopic 

 constituents more or less resembling the sacs or cells just re- 

 ferred to in the potato. Tbese are the final points at which we 

 arrive in our dissection or anatomical analysis of organic struc- 

 tures. Hence we term them the elementary organs, for, like the 

 large and conspicuous organs, they have a definite and charac- 

 teristic form and construction, while they cannot be subdivided 

 without passing from the condition of organs into that of mere 

 oro:anic substances. The larijer organs verv commonlv contain 

 several different kinds or forms of elementary organs in their 

 composition ; these, however, are not then intermixed at random, 

 hut combined according to particular laws of arrangement. Such 

 collections of elementary organs, known by the name of tissues, 

 are divisible into simple and complex tissues, according as one 

 or more kinds of elementary organ enter into their construction. 

 In animals, where the functions are multifold, diverse, and much 

 localized, the modifications occurring among the elementary 

 organs are very important and the tissues very distinct in 

 character. In the higlier animals, moreover, the large organs are 

 so individualized that the broad general laws of pliysiology may 

 be comprehended without much acquaintance witli the pheno- 

 mena occurring in the minute structures, on which, jiowever, 

 these same laws are ultimately founded. 



In plants, on tlic contrary, the functions are not only much 

 more simple, but they are even to a great extent diffused through- 

 out the whole frame, and almost any part may be modified by 

 circumstances so as to perform any function. In ac. ordancc 

 with this, the elementary organs do not display that diversity 



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