504 LECTURE XXI. 



physiological processes, how great an effect is produced by any disturbance 

 in the functions of the stomach. It is now clear to us that severe gastric 

 disturbances may be brought about by purely nervous influences without 

 there being organic changes. It is easy for us to believe that a hyper- 

 secretion may be produced by a condition of stimulation, caused, for 

 example, by a supersensitiveness of the secretory fibers of the vagus. On 

 the other hand, the experience of Pawlow and his school indicates the possi- 

 bilities of conditions of restraint with a limited supply of secretion. The 

 fact that the cells of the stomach glands are extremely sensitive to chem- 

 ical stimulation, and adjust themselves to the nature of the nourishment 

 with regard to their entire activity, enables us to understand that under 

 pathological conditions it is not necessary for the amount of secretion to 

 have become decreased or increased. Disturbances may arise which affect 

 the production of some particular substance. It is perfectly clear that 

 under such conditions the entire adjustment of the secretion to the nour- 

 ishment would be affected. Thus, normally, for the digestion of bread, 

 but little hydrochloric acid is present in the stomach during the entire 

 duration of the secretion. There is, to be sure, a reason for this, for by this 

 means the digestion of starch by the diastase in the saliva will continue 

 much longer. 



It is absolutely necessary that we should give prominence to the researches 

 of Pawlow in our study of digestion in the stomach. By means of 

 them, all the observations which have served for a long time to establish 

 the existence of characteristic sense-nerves, may be applied likewise to the 

 inner vation of the intestinal canal and its glands. These organs also 

 do not react fully by means of a single stimulation. Here again the stim- 

 ulation is only taken up by certain definite cells and transmitted in a 

 perfectly definite manner. The results of Pawlow's experiments are not 

 at all astonishing. We may assume that purely chemical processes play 

 a prominent part here. We may imagine that a certain kind of cell is 

 adjusted so that it is susceptible to a given chemical stimulation, while 

 a different cell is affected by another chemical substance. We may per- 

 haps apply the facts that we have established in the study of ferments 

 directly to the cells as a whole. The ferments are likewise products of 

 the cells. The individual cells produce them in such a way that they 

 possess certain groups which can react only with definite compounds 

 corresponding to a characteristic grouping. Conversely, the cells may be 

 so constructed that their function as a whole only appears when started 

 by the action of certain definite substance. 



The more extensive our knowledge becomes, and the more we enter 

 into the secrets of the metabolism of cells, the better we become con- 

 vinced that the cells themselves act by means of ferments. They do not 

 part with such ferments, but retain them for their own use. These cell- 



