THE DIGESTIVE TRACT OF ELASMOBRANCHS. 19 
earried on with the aid of pancreatic infusions as well as of small quantities of 
pancreatic juice obtained from hens and geese, that this secretion possesses powerful 
diastatic properties. 
As pointed out by Gamgee (1893, p. 203), this discovery of the sugar-forming 
enzyme of the pancreas has been erroneously attributed to Valentin (1844). Valentin 
recognized that starch was changed, but did not say that the change was a conversion 
to sugar. His own words are: “Wi ie man sieht erlauben diese Erfahrungen noch 
keine irgend bestimmenden Schliisse. Héchstens deuten sie darauf hin, dass viel- 
licht dic Panereastliissigkeit die Fiihigkeit habe die Stiirke léslich zu machen und 
beweilen eine Umsetzung derselben einzuleiten.” No further study of the pancreas 
seems to have been made until Bernard took up the work. 
Bernard (1856), by means of a pancreatic fistula, proved that the secretion is an 
alkaline fluid with a threefold action on starches, fats, and proteids. He concluded, 
however, that the pancreatic juice alone has no action upon proteids, but that it is 
able to dissolve them either when they have been first of all subjected to the action 
of bile or when it acts in conjunction with bile. To this proteolytic function of the 
pancreatic juice, indeed, Bernard gave little weight. 
In 1857 Corvisart called attention to the proteid-digesting power of the pancre- 
atic juice, and although his observations were more or less discredited by some, they 
were confirmed by Meissner (1859), Danilewsky (1862), and Kiihne (1867), the latter 
particularly contributing greatly to our knowledge of tryptic digestioa. 
The great interest awakened in the proteolytic activity of the pancreas by the 
researc hes of Kiihne (1867) was intensified by the publication of a remarkable memoir 
by Heidenhain (1875). In this paper the author described for the first time those 
changes in the secreting cells of the pancreas which correspond to the different states 
of activity, and announced that the fresh pancreas does not contain the proteolytic 
ferment, but an antecedent body which he called zymogen. This zymogen he found 
could be extracted from the gland, and under suitable treatment would yield the 
proteolytic ferment. Since Heidenhain’s discovery the antecedent bodies of other 
enzymes have been discovered. To the antecedent of the proteolytic enzyme of the 
pancreas, trypsin, the name trypsinogen has been given. 
Asa result of the study of the pancreas by the various investigators, this organ 
has long been known to secrete an alkaline juice and three enzymes or their 
zymogens, namely, trypsin, acting on proteids; amylopsin, acting on starches; and 
steapsin or lipase, acting on fats. Notwithstanding all the study of the pancreatic 
juice, however, in many ways the knowledge of its action was somewhat uncertain. 
Sometimes the pancreatic extracts would show a little digestive power, while the 
juice collected by a fistula was, as a rule, inactive. To explain these variations, 
investigations were made on the correlation between the pancreas and other organs 
and juices. Heidenhain (1875) had observed that when an aqueous solution of dried 
pig’s bile was added to a glycerin extract of the panentes the proteolytic power of 
the latter was increased. Chittenden (1885) noticed that bile in a pancreatic extract 
containing salicylic acid increased tryptic action. Martin and Williams (1890) and 
Rachford and Southgate (1895) also noticed the stimulating action of bile on tryptic 
digestion. Chittenden and Albro (1898), however, found that normal bile exerts 
very little influence on pancreatic proteolysis and may retard as well as aid. Bruno 
