LECTURE IV. 



Delivered on June 2gth. 

 THE CHEMICAL CORRELATIONS INVOLVING GROWTH OF ORGANS. 



MR. PRESIDENT AND GENTLEMEN, The chemical adaptations of the 

 body, which I have discussed in my first three lectures, have been almost 

 exclusively in the direction of increased activity of the responding organ. 

 One cannot, however, draw a sharp line between reactions involving 

 increased activity or dissimilation and those which involve increased 

 assimilation or growth, since under physiological circumstances the latter 

 is always the immediate sequence or accompaniment of the former. It is 

 a well-known fact that the best method of producing hypertrophy of any 

 organ is by increase of its physiological activity, and a good example of 

 the coincidence of assimilative with dissimilative changes is afforded by 

 the action of one of the hormones namely, secretin on the pancreas. 

 The most obvious result of injection of secretin is secretion of pancreatic 

 juice. If the animal is in bad condition, so that assimilatory changes are, 

 so to speak, handicapped, this increased activity of the pancreas is 

 attended by a total discharge of the zymogen granules, so that after a few 

 hours the gland on microscopic section is a typical discharged gland. 

 The discharge may go so far, as shown by Dale, that the ordinary secreting 

 cells of the gland lose not only their zymogen granules but also the main 

 part of their protoplasm and acquire the aspect and arrangement of the 

 cells which are familiar as forming part of " Langerhans' islets." If, how- 

 ever, we are dealing with an animal in good condition and are using a 

 preparation of secretin free from harmful admixtures, such as the de- 

 pressor substance usually present in extracts of the intestinal mucous 

 membrane, we may succeed in exciting a continuous flow of pancreatic 

 juice for some hours without inducing any change in the aspect of the 

 gland, microscopic sections at the end of four or five hours' continual 

 secretion presenting the typical aspect of a resting gland. In this case 

 the stimulus exciting to activity has at the same time directly or indirectly 

 called forth a corresponding building up of protoplasm and secretory 

 granules. The division of the chemical adaptations which we have 

 adopted must, therefore, relate solely to the primary effect of the excita- 

 tion involved. In the cases hitherto studied the primary effect has been 

 katabolic or increased activity. In the cases I shall bring before you 

 to-day the primary effect of the chemical stimulus is anabolic. We must 

 not, however, expect that the anabolic stimulus will diminish permanently 



