LECT. III.] GENERAL FLUID COMPONENTS. 119 



" the sap, after it has been exposed to the air, and 

 " light, in the leaf, and is returning from it to 

 " form the different secretions." The organs by 

 which the secretion is performed are probably 

 glands, which we have already endeavoured to 

 prove exist in vegetables ; and the secreted fluids 

 themselves are deposited in cells in different parts 

 of the plant, particularly in the bark, and the 

 roots ; these parts acquiring different medical vir- 

 tues, from the matters thus lodged in them. 



It is almost as impossible to obtain the proper 

 juice of plants free from sap, as it is to procure 

 the sap free from the proper juice ; this, however, 

 in the season in which it can be obtained in most 

 abundance, is not so liable to be diluted or mixed 

 with sap as at other times ; and therefore it is in 

 the warmest times in summer, that it ought to be 

 taken for the purpose of examining its properties- 

 Some naturalists have, rather fancifully, drawn a 

 very close analogy between it and the blood of 

 animals. Thus Rafn, with a microscope magnifying 

 135 times, supposed that he could detect round 

 globules, resembling the red globules of the blood, 

 swimming in a clear fluid, in the juice of Euphorbia 

 palustris; and Fontana thought he observed them 

 in the sap of Rhus toxicodendron. But such obser- 

 vations, which are often the effect of optical decep- 

 tion, are of little value, even admitting their va- 

 lidity, in a physiological point of view. In an 



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