11 



normally. When only tbe absolutely necessary minimum of one of the 

 nutrients is otl'ered a certain surplus of some of the others must be 

 present. 



THE LOW ATOMIC WEKIHT OF THE MINERAL NUTRIENTS. 



A review of the elements necessary for organic life shows at once 

 that they have low atomic weights, iron, with an atomic weight of 56, 

 having the highest among them. This is due, according to Leo Errera, 

 not only to their more fre([uent occurrence in the various compounds 

 making up the earth's crust, but also to their higher specilic heat. Thus 

 water, constituting as a rule two-thirds to three-fourths and sometimes 

 even more of the weight of a living organism, has the highest specitic 

 heat of all substances, consequently it can diminish the etlects of rap- 

 idly changing temperatures upon life. 



THE PHYSIOLOGICAL ROLE OF PHOSPHORIC ACID. 



RELATION OF PHOSPHORIC ACID TO PROTEIDS AND TO THE DIVISION 



OF CELLS. 



Phosphoric acid is, above all, necessary for the formation of lecithin' 

 and the nucleoproteids, e.g., chromatin- and plastin— the most essential 

 constituents of the nucleus and plastids. This makes clear the state- 

 ment of former writers, that phosphoric acid "follows the proteids," 

 since every new cell requires them. Wherever phosplioric acid is 

 transformed from the dissolved condition to an insoluble (compound, as 

 in the formation and growtli of the nucleus, fresh quantities must move 

 thither, according to the law of diffusion. The embryos can develop 

 by cell division only when phosphates are stored up in suflBcient quan- 

 tities in the seeds for the formation and increase of the nuclear sub- 

 stance in the new cells. Phosphoric acid, further, is not only contained 

 as calcium and magnesium phosphate in the globoids, but is also dis- 

 tributed in the seeds as dipotassinm phosphate. 



The observation that the total mass of protein in seeds is increased 

 by an increased supply of phosphoric acid would also be easily under- 

 stood on the basis of the hypothesis of ytrasburger and Sclimit<c that 

 the nuclei are the manufacturers of the protein matter. Tliis hypothe- 

 sis is highly probable, and in fact has been confirmed by Hofer in the 

 case of enzyms,' which must be considered as a class of proteins. 



'Two other phosphoric acid compounds, which are, however, restricted to the higher 

 auimals, are jecorin and inosic acid, the latter probably being merely a product of 

 metabolism. Besides phosphoric acid, the latter yields on decomposition hypo- 

 xanthin and probably trioxyvalerianic acid (Heuser). Another compound, thus far 

 encountered in plants only, yields, besides phosphoric acid among other things, iuo- 

 site (Schulze and Winterstein). 



"The nuclein extracted from organized structures is essentially an altered chro- 

 matin. 



3 Sitzungsberichte der Morph. Physiol. Ges., Miinchen, 1889. 



