SECTION 12 



THE METABOLISM OF LIPOIDS, STEROLS, CYCLOSES, 

 PHOSPHORUS AND SULPHUR 



12- 1. Phosphorus Metabolism of the Avian Egg 



The study of the distribution of phosphorus in a Hving system is 

 important for it exists in so many types of compound — Hpoids, 

 phosphoproteins, nucleoproteins, hexosephosphates, etc. — that a re- 

 markable survey of wide tracts of the mechanism of the egg can be 

 obtained by simply observing where the phosphorus is. It is for this 

 reason that the paper of Plimmer & Scott in 1909 may be called 

 classical, for it threw more light on the complex transformations going 

 on during the incubation of the hen's egg than any other single paper 

 before or since. It is true that they were not the first to study the 

 behaviour of the phosphorus fractions during development, for already 

 in 1877 Hoppe-Seyler had estimated the phosphorus in the yolk, and 

 had calculated thence the lecithin. He deserves much credit as being 

 the first to approach these problems from the quantitative point of 

 view, but his results are of little more than historical interest. Then 

 in 1893 Maxwell went into the subject again. He seems to have been 

 in the grip of a preconceived theory associated with work on plants, 

 and he certainly had the misfortune to use untrustworthy methods, 

 but he succeeded in showing that hpoid phosphorus preponderated 

 at the beginning of development, and non-lipoid phosphorus at the 

 end. 



% of the total phosphorus 



Ether-soluble Not ether-soluble 



Beginning 58-5 41-5 



End ... ... ' 27-0 73-0 



The rest of Maxwell's figures compressed great variations into a mini- 

 mum of data, and did not invite a beHef in their reliabiHty. Worse 

 still, he counted the phosphorus in the vitelHn as "mineral" phos- 

 phorus. In 1908 a much better piece of work was done by Carpiaux, 

 who observed an increase of inorganic phosphate during develop- 

 ment at the expense of the ether-soluble phosphorus. He defined 



