THE BIO-CHEMISTRY OF ANIMALS AND PLANTS 689 



proportions, of water under increased pressure, of oxidising and 

 reducing agents, etc. Of all these methods two have led to the 

 most constant and useful results — namely, hydrolysis by means 

 of ferments and by dilute mineral acids — and these methods 

 play at present a most important role in protein chemistry. 

 Whilst the last method has led to a knowledge of the final 

 cleavage products, the intermediate substances, which still show 

 protein characters, have been made available for further study 

 by the use of enzymes. The well-known stages of enzyme 

 action are the albumoses or proteoses, the peptones and amino 

 acids. Only quite recently E. Fischer has demonstrated an 

 intermediate stage between the peptones and the amino acids 

 by the isolation of the so-called polypeptides, which promise to 

 be of the highest importance for the chemistry and biology of 

 the proteins. 



The ideal aim of the chemist would be to separate the 

 complex mixture of cleavage products quantitatively in such a 

 way as to account for the whole of the carbon, nitrogen, and 

 sulphur in the original protein. This idea will, however, pro- 

 bably never be attained on account of the secondary reactions 

 taking place during hydrolysis, such as formation of brown and 

 black pigments, splitting off of C0 2 , etc. Even with the best 

 methods at his disposal, E. Fischer has succeeded so far only 

 in separating at the utmost 50 to 70 per cent, of the amino 

 acids present in the cleavage products. 



Under these circumstances it is of the greatest value to be 

 able to obtain by a short and reliable procedure at least an 

 approximate knowledge of the nitrogen distribution in the 

 protein molecule, even if this does not allow us to determine 

 quantitatively the single cleavage products. Such a method 

 has been worked out, mainly in Hofmeister's laboratory, by 

 Hausmann, and has been subsequently found trustworthy by 

 Osborne and others. 



Hausmann's method is shortly as follows : The whole nitrogen 

 of the protein is estimated by Kjeldahl's method. A weighed 

 amount of the substance is then hydrolysed by means of hydro- 

 chloric acid. After complete hydrolysis the cleavage products 

 are separated into three classes, and the nitrogen estimated in 

 each by means of Kjeldahl's method as — 



1. Amide-N or ammonia nitrogen. This comprises the 

 nitrogen of that part of the protein molecule which is easily 



