CHAPTER VI 



SECBETION AND GLANDULAR MECHANISMS 



Correlation of Secretion, Absorption, and Excretion, and their Relation- 

 ship to Osmotic Energy. The processes of secretion, absorption, 

 and excretion are distinguished from one another only by their 

 object or physiological function, and not by anything intrinsically 

 different in their nature or in the mechanism by which these 

 processes are carried out in the body. The purpose of secretion 

 is to prepare, an active substance in solution for use in assisting 

 a process which is of service to the organism in some other part, 

 such as a digestive secretion ; a secretion of a substance which 

 has a guiding influence upon chemical change in other tissues, 

 and hence affects the state of activity of those tissues, as, for 

 example, the internal secretions, adrenalin, secretin, &c. ; or a 

 secretion which acts by mechanical means, such as the secretion 

 of the tears in the lachrymal gland, the mucous secretions on the 

 mucous surfaces, and the serous and synovial secretions of the 

 serous and synovial cavities. The purpose of absorption is to 

 take up for the service of the body generally and of the absorbing 

 cells the materials in solution which have been prepared and 

 modified by the secretions. Lastly, the purpose of excretion is 

 to remove from the body materials which have passed through, 

 or been formed in, the cycle of metabolism in the body, and have 

 become waste products for which the body has no further use. 

 In addition, the purpose of excretion is to maintain in normal 

 amount and concentration in the circulating fluid of the body, 

 the blood, those products which are of service, for in abnormal 

 concentrations these useful bodies become as injurious to the 

 living cells as effete products of metabolism, or foreign sub- 

 stances of actively poisonous nature. 



Respiration also is essentially identical in its nature with these 

 three processes, being a combination of absorption, secretion, 

 and excretion, the only differencs being that the products con- 

 cerned in respiration exist in the form of gases before being taken 



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