1904.] The Chemical Regulation of the Secretory Process. 315 



which has been obtained in a crystalline form and the chemical 

 constitution of which has been approximately determined. This is, 

 indeed, what one would expect of a substance which has to be turned 

 out into the blood at repeated intervals in order to produce in some 

 distant organ or organs a physiological response proportional to the 

 dose. The bodies of higher molecular weight, such as the toxins, 

 which owe their activity, according to Ehrlich, to the fact that they 

 can be directly assimilated by the cells of the body, and built up 

 into the protoplasmic molecule, always give rise to the production of 

 anti-bodies, a process which, while not preventing necessarily their 

 utilisation in the body, would prevent their acting as a physiological 

 stimulus to certain definite cells. Adrenalin and secretin on the 

 other hand belong to the class of drugs which act by their physico- 

 chemical properties, and whose physiological effect is determined by 

 the total configuration of their molecule. It was suggested to us 

 early in our experiments that the secretion of pancreatic juice, evoked 

 by secretin, was essentially a sudden production of an anti-body ; 

 such a sudden production is unknown in the animal body, and the 

 anti-character of the secretion is at once negatived by the fact that 

 secretin can be mixed with a freshly secreted juice without in any way 

 destroying its efficiency. 



Like adrenalin, secretin is extremely easily oxidised, and it is 

 probable that it is got rid of in this way from the body, since, even 

 after repeated injections of secretin, it is impossible to find this 

 substance or any precursor of it either in the pancreas, the urine, or 

 other tissues of the body. Just as in the case of adrenalin, so we 

 find that secretin is not specific for the individual or species. An 

 extract of the mucous membrane of the dog will evoke secretion in the 

 pancreas of the frog, the bird, rabbit, cat, or monkey. In the same 

 way the pancreatic secretion of the dog can be excited by injection 

 of secretin prepared from the intestine of man, cat, monkey, rabbit, 

 fowl, salmon, skate, frog, or tortoise. The evolution of this mechanism 

 is, therefore, to be sought at some time anterior to the development of 

 vertebrates. 



The action of secretin is not confined to the pancreas. It has long 

 been known that the pancreatic juice, in order to exert its full 

 activity on the food stuffs, needs the simultaneous presence of bile, 

 and the fact that in many cases the two fluids are poured into the 

 duodenum by a common orifice shows the close connection which 

 must exist between them. Digestion of fats is impossible unless both 

 fluids have access to the gut, and even in the digestion of carbo- 

 hydrates, as was shown by S. Martin and Dawson Williams many years 

 ago, the presence of bile greatly hastens the digestive powers of the 

 pancreatic juice. Whenever, therefore, a secretion of pancreatic juice 

 is required, a simultaneous secretion of bile is also necessary. It is 



