710 PRINCIPLES OF GENERAL PHYSIOLOGY 



distinction drawn between excitants such as hydrochloric acid, which enable 

 secretin to be absorbed, and those above named, which produce it, but without 

 enabling it to be absorbed, is not a valid one. In a further paper (1912, 2) 

 Lalou investigates the behaviour of secretin towards chemical agents, with a view 

 to elucidating its nature. The most interesting fact is that it is rapidly destroyed 

 by pancreatic and gastric juices, by erepsin in neutral solution, and by pa pain. 

 In connection with this fact, a discovery by Delezenne and Pozerski (1912) is 

 of interest. They showed that extracts of various tissues containing erepsin, 

 especially the mucous membrane of the intestine, have a powerfully destructive 

 action on secretin. This fact has to be kept in mind when extracting the mucous 

 membrane with cold water. 



Gley (1-912) gives a classification of the various chemical excitants of pancreatic 

 secretion. 



The complete proof that secretin is present in the blood of an animal after 

 the introduction of acid into the duodenum was given simultaneously by Fleig 

 (1903) and by Enriquez and Hallion (1903), who found that the blood of a dog, 

 in which pancreatic secretion had been induced by the introduction of acid into 

 the duodenum, was capable of producing activity of the pancreas in a second dog. 



Gastric Secretion. The observations of Pavlov showed that the introduction of 

 meat into the stomach caused secretion in an isolated small stomach, even when 

 nervous influences were excluded. Edkins (1907) showed that extracts of the 

 pyloric mucous membrane, made in various ways, but especially by the action 

 of dextrine, caused increased formation of an acid gastric juice. Maydell (1913) 

 confirmed the fact, in so far as that subcutaneous injection of extracts of pyloric 

 mucous membrane brought about increased secretion in a dog with a chronic gastric 

 fistula. The most active preparation was found to be made by extracting pyloric 

 mucous membrane with 0'4 per cent, hydrochloric acid at ordinary temperature. 

 Immediately before injection this was neutralised. Extracts of other parts of 

 the stomach or of the duodenum were ineffective. Comparing the properties of 

 the juice obtained from the same animals by " sham feeding," that is, the juice 

 obtained by natural stimulation of the vagus, the acidity was found to be about 

 the same ; the digestive power was, however, considerably less in secretion 

 obtained by chemical agency. Maydell was able to obtain a dry active pre- 

 paration by the application of Stepp's method, described above for the pancreatic 

 secretin. 



Adrenaline. Brief reference has been made already to the action of the 

 product of activity of the suprarenal glands. The first investigation of the 

 properties of this substance was made by Oliver and Schiifer (1895), in so far 

 as concerns extracts of the organs. They showed also that' the pressor substance 

 is contained in the medulla only. The active principle, "adrenaline," was isolated 

 by Takamine (1901) and found to be 



H0_ 

 HO/ \-CH (OH)CH 2 NHCH 3) 



and may be regarded as a methyl-amino derivative of pyrocatechol. Since this 

 contains an asymmetrical carbon atom, there are two optical isomers. In the 

 suprarenal glands the /-form only occurs. The racemic mixture has been pre- 

 pared synthetically by Stolz (1907), and found to be rather more than half as 

 active as the natural form ; hence the d-isomer is much less active than the 

 /-isomer. An instructive case of similar difference of activity in optical isomers 

 will be referred to in the case of hyoscine on a later page. 



The similarity of the structure of adrenaline to that of tyrosine or homogentisic 

 acid (see page 432 above) will be noticed, and it has been stated that the 

 suprarenal gland mixed with tyrosine in vitro is able to produce adrenaline from 

 the amino acid ; but further investigation failed to confirm the statement. 



The occurrence of adrenaline in the secretion of the " parotoid " glands of 

 a toad, described by Abel (1913), indicates that it may be a more or less accidental 

 product of metabolism in itstirst appearance. 



