The facts presented are the result of eight experiments essentially run exactly in the same way, according to the method described [above]:
Accordingly we consider as proved:
This also would provide a natural explanation for the origin of the so-called 'loosely bound nitrogen' of the protein substances, on which repeated remarks have already been made and the exact quantitative estimation of which O. Nasse only recently undertook again.
It is the nitrogen of the NH2 group which comes from compounds like asparagine and glutamine in the form of ammonia, when aspartic acid and glutamic acid are formed.
Compounds of this kind, which on boiling with acid or alkali lose ammonia and yield these acids with uptake of water, must in general be considered pre-existent in casein and the protein substances.
Whether these are identical with the customary asparagine and the still to be prepared homologous glutamine, and whether the acids obtained are not products of a molecular re-arrangement and shifting, cannot be decided at present.
We have also investigated the breakdown of protein substances according to our method with albumin, legumin and the plant albumin, and the qualitative result was the same as with the casein.
We further endeavoured to find a quantitative expression for this manner of breakdown; but we have still not succeeded in separating and estimating the amounts of the single breakdown products with the desired exactitude.
Only this we can state on the grounds of numerous already collected data that the different protein modifications yield different amounts of these products, and it appears to us now already as more than a mere guess that the differences in the properties of the protein modifications are to be sought in a different proportion of the primary atom groups of which they are constituted.
Pflüger's Archiv für Physiologie 6, 589; 7, 139. [original note]