48 INORGANIC FOODSTUFFS 



of hemoglobin, the pyrrole radical. Chlorophyll, it is true, is indigest- 

 ible by the digestive juices, but it is split up by the bacteria which 

 inhabit the intestine, and in this way a portion of the pyrrole which it 

 contains may possibly be rendered available for assimilation from the 

 intestine and utilization by the tissues. 



It will be recollected that if iron is administered to young animals 

 which are undergoing iron-starvation by being kept upon an exclusive 

 milk-diet, their growth is markedly accelerated despite the fact that 

 the iron is not utilized to build up hemoglobin. This effect is of sig- 

 nificance, inasmuch as it indicates that iron subserves other important 

 functions in the body besides that of entering into the composition 

 of the oxygen-carrying pigment of the blood. We are reminded of the 

 prevalence of iron in nuclear elements, and led to suspect that iron 

 plays some essential part in the functions of the nuclei. It is a note- 

 worthy fact, however, that if iron be added, in similar amounts to those 

 employedjn the above-cited experiments, to an abundant and mixed 

 diet, containing a normal sufficiency of iron, this acceleration of growth 

 is not observed. Evidently beyond a certain diurnal allowance the 

 tissues of the growing animal are not able to utilize iron for the purposes 

 which result in the acceleration of growth. Here we meet again with a 

 phenomenon to which reference was made in connection with the utili- 

 zation of calcium. The ability of the tissues to profitably utilize the 

 materials brought to them sets a definite limit to the amount of a food- 

 stuff which it is of any avail to consume. It is doubtless for this 

 reason that iron, whether in the organic or the inorganic form, is with- 

 out effect in accelerating the rebuilding of hemoglobin after hemor- 

 rhage. The blood-forming tissues are able to manufacture so much 

 hemoglobin per diem and the supply of more raw materials than they 

 can "work up" in a day is useless. 



The ultimate reason for this phenomenon, which is of such general 

 occurrence in life-phenomena, resides undoubtedly in the multifarious 

 variety of the chemical processes which underlie and accompany vital 

 activities. In every detail of change which accompanies the per- 

 formance of any function by living tissues not merely one chemical 

 reaction is involved but a whole series of interwoven reactions following 

 and depending upon one another. Now in any series of chemical 

 changes of which the second utilizes some product of the first, the third 

 some product of the second, and so forth, it is always the specifically 

 slowest reaction which "sets the pace" for those which succeed it. 

 No matter how quickly raw materials may be supplied, this "master- 

 reaction" can proceed only at a certain maximum speed and succeeding 

 reactions must wait for its products before they can seize and elaborate 

 them. Provided then, that any article of diet be supplied in sufficiency 

 to maintain at top speed the "master-reaction" of the series of pro- 

 cesses intojwhich it enters, excess of this particular item in the dietary 

 is mere wastagejand casts an unnecessary strain upon the organs of 

 elimination. 



