1 66 SCIENCE PROGRESS 



merely depolymerise the proteid molecule, but breaks it down 

 into heterogeneous fractions [Pick]. We know that the activised 

 trypsin of the pancreatic juice is capable by itself of producing 

 a more complete breakdown than was earlier thought [Kutscher], 

 and the physiological succession of peptic action, followed by 

 tryptic action, is an ordered arrangement making for still greater 

 efficiency in the process of hydrolysis [Fisher and Abderhalden]. 

 Lastly, we know that the intestinal cell contains, and to some 

 extent secretes, a ferment — erepsin — which has a potent influence 

 in promoting hydrolysis at its final stages [Cohnheim]. The 

 existence of such an array of proteoclastic agents might conceiv- 

 ably be explained on other grounds ; but a frank recognition of 

 the facts certainly leads to the view that a more or less complete 

 breakdown of our nitrogenous foodstuffs in the gut is a physio- 

 logical necessity. 



Again, if the full significance of the specificity of tissue 

 proteids has been grasped, implying as it does the necessity 

 of a re-moulding of the dietetic proteid, it will explain why 

 the intestinal breakdown should be profound — why something 

 more is required of the gut than the mere production of soluble 

 absorbable material. There has to be a change in the archi- 

 tecture of the proteid, and we may here use an analogy, and 

 urge that if, for instance, a gothic cathedral had to be constructed 

 out of a classic temple, the latter would need first to be 

 disintegrated well-nigh into its constituent stones. 1 In the 

 simpler case of carbohydrate metabolism, the vegetable starch 

 has to be broken down into sugar before it receives the stamp 

 of animal life, and is resynthesised into glycogen ; the vegetable 

 proteid, on the other hand, has to obtain not merely the stamp 

 of the animal, but that of the species. 



Even in unicellular animals a mechanism for the breakdown 



of proteid before assimilation is always present, and in some 



species of amoeba it has been shown that ferments of the 



tryptic, or more destructive type, are present [H. Mouton], 



and during the digestive processes of other protozoa the reaction 



of the fluid in the vacuoles also indicates that a tryptic ferment 



1 This analogy, or something like it, has now been frequently used, and the idea 

 it illustrates is common property ; but, to the best of my belief, it was first em- 

 ployed in this connection by the late Professor Huppert of Prague, who luminously 

 wrote upon the importance of chemical differentiation in animal species, long 

 before the subject received general attention {Ueber die Erhaltung der Arteigen- 

 schaften, Prag, 1896). 



