346 THE VITAL FUNCTIONS. 



remains involved in nearly the same degree of 

 obscurity as at first.* It was natural to expect 

 that in this inquiry material assistance would be 

 derived from an accurate anatomical examina- 

 tion of the organs by which the more remarkable 

 secretions are formed ; yet, notwithstanding the 

 most minute and careful scrutiny of these organs, 

 our knowledge of the mode in which they are 

 instrumental in effecting the operations which 

 are there conducted, has not in reality advanced 

 a single step. To add to our perplexity we often 

 see, on the one hand, parts, to all appearance 

 very differently organized, giving rise to secre- 

 tions of a similar nature ; and on the other hand, 

 substances of very different properties produced 

 by organs, which, even in their minutest details, 

 appear to be identical in their structure. Secre- 

 tions are often found to be poured out from 

 smooth and membranous surfaces, such as those 



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

 of secretion are immediately instrumental in producing the sub- 

 stance 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 sponta- 

 neously forming in that fluid in the course of its circulation. 

 This hypothesis, in which the glands, and other secreting appa- 

 ratus are regarded as only very fine strainers, is supported by a 

 few facts, which seem to indicate the presence of some of these 

 products in the blood, independently of the secreting processes 

 by which they are usually supposed to be formed ; but the evi- 

 dence is as yet too scanty and equivocal to warrant the deduc- 

 tion of any general theory on the subject. 



