ELEVENTH LECTURE. 



THE PHYSIOLOGY OF SECRETION. 



A. MATHEWS. 



When a substance contained in protoplasm leaves it, it is 

 said to be secreted, or separated from it. As all forms of pro- 

 toplasm are constantly giving off matter of one kind or another, 

 all cells are true secreting cells. Such secretion is an attribute 

 of all living matter. 



The word "secretion," as it is ordinarily used, however, is 

 made to designate something more than this simple process of 

 separation ; it is intended to include also the process of manu- 

 facture by the cell of the substances thrown off. It is unfor- 

 tunate that the same name has been given to two such different 

 processes as those of secretion and manufacture, and it is not 

 surprising that this has resulted in great confusion. In the 

 present paper we shall deal solely with the separation of sub- 

 stances from the cell. I shall use the word " secretion " to mean 

 this and nothing more, unless, as will be specially stated, it be 

 used to cover the discharge from the gland duct as well. The 

 process of the manufacture of substances by the cell I have 

 elsewhere proposed to call "hylogenesis," literally meaning 

 the formation of substance. This process will not be specially 

 considered here. 



How do the substances formed by protoplasm escape from it ? 

 This is accomplished in a variety of ways, depending upon 

 whether the substances are of small molecular size and soluble, 

 or whether they are complex bodies. Soluble substances of 

 small molecular size escape from the cell by osmosis. Such is 

 the case, for example, for all gases, such as hydrogen, sulphu- 



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