TRANSFERENCE OF FOOD MATERIALS 127 



of enterokinase already present in the pancreatic juice. The 

 alkalinity of the solution makes a great difference to the rate of 

 activation by enterokinase and neutralisation increases the 

 rate of activation. Thus if the pancreatic juice is neutralised 

 an amount of enterokinase, insufficient to cause rapid activa- 

 tion, can cause activation. The neutralisation is brought 

 about by the interaction of the calcium salts with the sodium 

 carbonate in the pancreatic juice, whereby calcium carbonate 

 is precipitated. 



CaCl 2 + Na 2 CO 3 = 2NaCl + CaCO 3 



The curve of activation is peculiar in that the rate increases 

 as the reaction proceeds. Vernon believes that this is due to 

 an unstable form of trypsin produced by the action of enter- 

 okinase and that this unstable form activates the trypsinogen.* 

 Mellanby and Woolley, on the other hand, consider that the 

 increase in rate of activation is not due to an unstable form of 

 trypsin. f It seems possible that if trypsin is produced it will 

 act upon proteins, converting them into amino acids. The 

 amino acids can neutralise the alkali of the pancreatic juice, 

 and as mentioned above neutralisation increases the rate of 

 activation. Hence the increase in rate of activation may be 

 due to a neutralising of the pancreatic juice by the products of 

 protein digestion produced by the trypsin formed during the 

 earlier stages of activation. 



The methods for estimating the rate of digestion of protein 

 have been mentioned in connection with pepsin, but one 

 method applies to trypsin which does not give good results 

 with pepsin. Formaldehyde condenses with ammonia com- 

 pounds to form hexamethylene tetramine and with amino 

 acids to neutralise the amine group. This forms the basis 

 of a method to estimate the amount of amine groups set free 

 by digestion, as each splitting of a CO NH group gives rise 

 to a fresh NH 2 group. The solution is neutralised to 

 phenolphthalein and neutral formaldehyde is added. The 

 combination of formaldehyde with the NH 2 groups causes the 

 amine group to lose its alkaline character, hence the carboxyl 

 group becomes predominant and the amino acid becomes a 

 stronger acid ; the amount of alkali required to neutralise these 

 acids gives an indication of the amount of amino acids in the 

 solution. As the amino acids increase in amount during 



* H. M. Vernon, Jonm. Physiol., 1902, vol. 27, p. 269. 

 f J. Mellanby and V. J. Woolley, Joiwn. Physiol., 1913, vol. 46, 

 P- 159. 



