330 PHYSIOLOGY CHAP. 



are eliiniuated by external secretion, also perhaps to a simultaneous 

 production of glycogen, which accumulates in the cytoplasm and 

 is slowly elaborated and poured out into the blood in the form 

 of glucose. Protein undergoes a different conversion in each 

 glandular organ that has a specific function. We are more or 

 less acquainted with the end-products of these hidden processes, 

 but of the intermediate links forged within _the cytoplasm we 

 know nothing. 



We do not know definitely whether the reserve protein of 

 alimentary origin is equally distributed throughout the whole of 

 the cytoplasm, or whether (as for fat and glycogen) there are 

 organs and tissues which store it up in larger amount, and may be 

 regarded as special reserves. It seems probable that the lymph 

 organs serve as such a storehouse, since, as Fredericq noted, they 

 shrink in volume more than the other organs during fasting 

 the liver excepted, which in starvation consumes the whole 

 of its stored-up glycogen, and is greatly reduced in weight and 

 volume. 



We know that vegetable protoplasm, either with or without 

 chlorophyll, is able to nourish itself and to develop, at the expense 

 of the materials which it draws from the inorganic world. Plants, 

 in other words, are capable of manufacturing by synthesis from 

 the elements, or the very simple compounds which they obtain 

 from the earth, air, and water, the whole of the organic substances 

 carbohydrates, fats, and proteins which enter into the composi- 

 tion of their tissues. Is it possible that the same phenomenon, in 

 a minor degree and starting from less simple compounds, takes 

 place in the animal organism also ? We have seen that animal 

 amylogenesis and adipogenesis can occur either by synthetic 

 processes, which start from the glucose, or by analytic processes, i.e. 

 cleavage of the protein molecule. Is animal protoplasm also able 

 to effect synthesis of the protein molecule from the nitrogenous 

 (amino-acids) and non-nitrogenous groups into which it has been 

 broken up ? 



The whole of the protein stored up in the animal body 

 is usually held to be of alimentary origin, the total nitrogen 

 eliminated in the urine being taken as the measure of its con- 

 sumption. But although this theory has been uncontested, it 

 is founded on no direct experimental evidence. It is not 

 so much a true scientific theory as a physiological dogma, 

 deduced from the ancient doctrine of the antagonism between 

 plant and animal organisms which is no longer tenable to-day. 

 When we discuss the metabolism which underlies muscular 

 activity and muscular work, we shall have to examine a fact which 

 seems to give countenance to this doubt, and to admit the 

 possibility of animal proteinogenesis. 



0. Loewi (1902) succeeded in giving a direct experimental 



