SECRETION. 245 



quently made to undergo in the course of circulation, and 

 when subjected to the action of the nutrient vessels and se- 

 creting organs; being ultimately converted into the various 

 textures and substances which compose all the parts of the 

 frame. All the modifications of cellular substance, in its 

 various states of condensation; the membranes, the liga- 

 ments, the cartilages, the bones, the marrow; the muscles, 

 with their tendons; the lubricating fluid of the joints; the 

 medullary pulp, of the brain; the transparent jelly of the 

 eye; in a word, all the diversified textures of the various 

 organs, which are calculated for such different offices, are 

 derived from the same nutrient fluid, and may be considered 

 as being merely modified arrangements of the same ultimate 

 chemical elements. 



In what, then, we naturally ask, consists this subtle che- 

 mistry of life, by which nature effects these multifarious 

 changes; and in what secret recesses of the living frame has 

 she constructed the refined laboratory in which she operates 

 her marvellous transformations, far surpassing even those 

 which the most visionary alchemist of former times had 

 ever dreamed of achieving? Questions like these can only 

 be fairly met by the confession of profound ignorance; for, 

 although the subject of secretion has long excited the most 

 ardent curiosity of physiologists, and has been prosecuted 

 with extraordinary zeal and perseverance, scarcely any po- 

 sitive information has resulted from their labours, and the 

 real nature of the process remains involved nearly in the 

 same degree of obscurity as at first.* It was natural to ex- 



"* It is not yet precisely determined to what extent the organs of secretion 

 are immediately instrumental in producing 1 the substance which is secreted; 

 and it has been even suggested that possibly their office is confined to the 

 mere separation, or filtration from the blood, of certain animal products, 

 which are always spontaneously forming in that fluid in the course of its 

 circulation. This hypothesis, in which the glands, and other secreting ap- 

 paratus are regarded as only very fine strainers, is supported by a few facts, 

 which seem to indicate the presence of these products in the blood, inde- 

 pendently of the secreting processes by which they are usually supposed to 

 i>e formed; but the evidence is as yet too scanty and equivocal to warrant 

 the deduction of any general theory on the subject. 



