LECTURE X. 



ALBUMINS OR PROTEINS. 

 IV. 



DEGRADATION AND FORMATION OF PROTEIN IN THE ANIMAL AND 

 VEGETABLE ORGANISMS. 



IT will be necessary to learn something about the origin of the proteins 

 in our food, before proceeding to discuss the behavior of such substances 

 when taken into the animal organism, their decomposition in the alimen- 

 tary tract, their absorption and assimilation, and the end-products result- 

 ing from their combustion. The animal organism, as we shall see later, 

 is only capable of synthesizing its albumins from the same material, or 

 from its immediate decomposition products. It is incapable of utilizing 

 inorganic nitrogenous compounds to produce its albumins, and similarly 

 the animal cells cannot synthesize the albumins from organic nitrogen- 

 ous substances, unless these are related directly to the albumins them- 

 selves. The animal organism is entirely dependent on the vegetable 

 kingdom for its albumin requirements. The plants prepare the proteins 

 for it. 



When living material, whether it be vegetable or animal, decays, its 

 organic constituents undergo putrefaction. Ammonia, in large amount, 

 is finally produced from nitrogenous compounds. This is changed into 

 nitric acid in the soil, nitrates resulting. The formation of saltpeter in 

 the soil is a process which has been known for a long time. Even H. 

 Davy l was aware of the production of nitrates at the expense of ammonia 

 and atmospheric oxygen. It was eventually discovered that the process 

 of forming saltpeter, also called " nitrification," was due to the vital 

 activity of microbes. The pure culture of these organisms followed much 

 later. 2 This was due to the fact that the bacteria possess the peculiar 

 ability of thriving on an exclusively inorganic nutrient medium, as was 

 shown by Hueppe 3 and Heraeus. 4 



They satisfy their nitrogen and carbon requirements from ammonium 



1 Elements of Agricultural Chemistry, 1814. 



2 S. Winogradsky: Compt. rend. 110, 1013 (1890). 



3 Tageblatt Naturforscher-Versammlung Wiesbaden, 1887. 



4 Zentr. Bakt. 3, Nr. 13 (1887). 



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