16 PHYSIOLOGICAL ROLE OF MINERAL NUTRIENTS. 



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 specific heat of all substances; consequently it can diminish 

 the effects of rapidly 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 a 

 and the nucleoproteids, e. g., chromatin 6 and plastin, the most essen- 

 tial constituents of the nucleus and plastids. This makes clear the 

 statement of former writers that phosphoric acid ''follows the pro- 

 teids," since every new cell requires them. Wherever phosphoric 

 acid is transformed from the dissolved condition to an insoluble com- 

 pound, as in the formation and growth of trie nucleus, fresh supplies 

 must move thither, according to the law of diffusion. The embiyos 

 can develop by cell division only when phosphates are stored up in 

 sufficient quantities in the seeds for the formation and increase of the 

 nuclear substance in the new cells. Phosphoric acid, further, is not 

 only contained as calcium and magnesium phosphate in the globoids, 

 but is also distributed in the seeds as dipotassium 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 Strasburger and Schmitz that 

 the nuclei are the manufacturers of the protein matter. This h} T poth- 

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

 the case of enzymes, 6 ' which must, partially at least, be considered as a 

 class of proteins. 



The yield of grain is much more increased by phosphoric acid than 

 by nitrogen or potassium compounds. 



In order to observe how a deficiency of phosphoric acid would inter- 

 fere with the normal action of plant cells the writer compared at a low 

 temperature the behavior of algae (/Spirogyra) in complete culture 



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

 higher animals, are jecorin and inosic acid, the latter probably being merely a prod- 

 uct of metabolism: Besides phosphoric acid, the latter yields on decomposition 

 hypoxanthin and probably trioxy valerianic acid (Heuser). Another compound, 

 thus far encountered only in plants, yields, besides phosphoric acid, inosite (Schulze 

 and Wintersteiri). This compound is considered by Posternak to be oxymethyl 

 phosphoric acid. 



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

 matin. It contains metaphosphoric acid (Liebermann). 



c Sitzungsberichte der Morph. Physiol. Ges., Munich, 1889. 



