148 THE SCIENCE OF BIOLOGY 



secretion, contains the parent chemical compounds out of 

 which the secretion is formed as it passes from the cell into 

 the central cavity. The gland-cell is like a factory, which 

 receives certain raw material delivered by a common carrier 

 at the back door, and transforms it into a product that is 

 passed out on the other side. The blood is the carrier of 

 raw material, which the gland-cells receive and which they 

 convert into the secretion exuded into the cavity of the gland 

 and thence passed to the outside. A substance like water, 

 which is, of course, present in all secretions, passes through 

 the cells unchanged. The substances distinctive of a partic- 

 ular secretion, and not present in the blood, must, obviously, 

 be manufactured within the gland-cells from material 

 received from the blood. The gland-cell, therefore, re- 

 sembles an industrial establishment engaged in the manufac- 

 ture of chemicals. Some of the physico-chemical processes 

 which occur in cells of this nature are well established. 

 Others remain to be discovered. No one claims that having 

 thus localized the formation of a secretion within the cell, 

 he has explained the ultimate vital phenomena. The point 

 is that in secretion, as in other vital processes, the structural 

 and so the functional basis for what goes on is a cellular 

 basis. The phenomena of muscle and nerve might be traced 

 in like manner to their cellular foundation. Structure and 

 function are everywhere explicable in terms of cells. 



The science of physiology was thus advanced from a study 

 of gross phenomena, such as the mass-contraction of a 

 muscle, the conduction of a nerve-impulse, or the simple 

 features of a process like secretion, to an examination of 

 cellular activities underlying the more obvious phenomena. 

 The publication of Verworn's classical work upon " General 

 Physiology/' 10 in which the problems of physiological 

 science were attacked as cell problems, expressed this prog- 

 ress from the study of functional activity in the mass to its 

 study within the cell. It also indicated the advance toward 



10 Verworn, M., "Allgemeine Physiologic," 1895. 



