451 COMPAEATIVE PHYSIOLOGY, 



maxillary gland have been divided, a flow of saliva begins and 

 is continuous till the secreting cells become altered in a way 

 visible by the microscope. Now, we have learned that proto- 

 plasm can discharge all its functions in the lowest forms ol 

 animals and in plants independently of nerves altogether. 

 What, then, is the explanation of this so-called '' paralytic se- 

 cretion " of saliva ? The evidence that the various functions 

 of the body as a whole are discharged as individual acts or 

 series of acts correlated to other functions has been abundantly 

 shown; and, looking at the matter closely, it must seem un- 

 reasonable to suppose that this would be the case if there was 

 not a close supervision by the nervous system over even the 

 details of the processes. We should ask that the contrary be 

 proved, rather than that the burden of proof should rest on the 

 other side. Let us assume that such is the case ; that the entire 

 behavior of every cell of the body is directly or indirectly con- 

 trolled by the nervous system in the higher animals, especially 

 mammals, and ask. What facts, if any, are opposed to such a 

 view ? We must suppose that a secretory cell is one that has 

 been, in the course of evolution, specialized for this end. What- 

 ever may have been the case with protoplasm in its unspecialized 

 form, it has been shown that gland-cells can secrete independ- 

 ently of blood-supply (page 314, etc.) when the nerves going to 

 the gland are stimulated. Now, if these nerves have learned, in 

 the course of evolution, to secrete, then in order that they shall 

 remain natural (not degenerate) they must of necessity secrete; 

 which means that they must be the subject of a chain of meta- 

 bolic processes, of which the final link only is the expulsion of 

 formed products. Too much attention was at one time directed 

 to the latter. It was forgotten, or rather perhaps unknown, 

 that the so-called secretion was only the last of a long series of 

 acts of the cell. True, when the cells are left to themselves, 

 when no influences reach them from the stimulating nervous 

 centers, their metabolism does not at once cease. As we view 

 it, they revert to an original ancestral state, when they per- 

 formed their work, lived their peculiar individual life as less 

 specialized forms wholly or partially independent of a nervous 

 system. But such divorced cells fail; they do not produce 

 normal saliva, their molecular condition goes wrong at once, 

 and this is soon followed by departures visible by means of the 

 microscope. But just as secretion is usually accompanied by 

 excess of blood, so most functional conditions, if not all, de- 



