280 THE PHYSIOLOGY OF REPRODUCTION 



by lecithin. Lecithin also absorbs oxygen very readily and becomes 

 oxidised even at room temperature. It has, therefore, many of the 

 properties which we associate with living protoplasm ; it may be said 

 to absorb food-stuffs and to assimilate them in the sense of altering 

 the properties of these food-stuffs ; it shows selective staining and 

 it absorbs oxygen. Some experiments of the writer, 1 carried out in 

 1908, suggest that these phosphorised fats may act as oxygen-carriers, 

 and that they may thus fulfil an important function in cell-respiration. 

 A similar view has been put forward also on purely theoretical grounds 

 by Mansfeld. 2 



However that may be, there can be little doubt that in the egg, 

 which contains an exceptionally large amount of phosphorised fats, 

 these substances have to fulfil a different function. Phosphorus 

 enters into the composition of many cell constituents, for instance 

 the complex protein substances found in the nuclei of cells, . the 

 so-called nucleoproteins, so that the assimilation of phosphorus is an 

 important factor in the growth of an organism. In birds the yolk 

 of the egg fulfils a function similar to that of the milk in Mammals ; 

 both supply the offspring with the material necessary for its growth. 

 We thus find that both the yolk and the milk are not only rich in 

 phosphorus, but that most of the phosphorus is present in organic 

 combination, as casein and nuclein in the latter, and as vitellin and 

 phosphorised fats in the former. 



It was held at one time that the organism could not synthesise 

 organic phosphorus compounds from inorganic phosphates. This has 

 been disproved by Gregersen, 3 who showed that animals can maintain 

 themselves in phosphorus equilibrium when inorganic phosphates are 

 the only source of phosphorus, provided that protein is also given. 

 Similarly the eggs of ducks fed on a diet containing only inorganic 

 phosphates were found to have a normal lecithin value. 4 It is 

 therefore not very obvious why both egg-yolk and milk should be 

 so rich in organic phosphorus compounds; it may lie merely to 



1 Cramer, Unpublished observations. It was found that watery emulsions 

 of egg-lecithin absorbed much more oxygen than water alone or watery 

 solutions of proteins, and that such a lecithin-emulsion sometimes greatly 

 accelerated the oxidation of hydriodic acid by the oxygen of the air. The 

 results", obtained were, however, very variable. Thunberg (Skandin. Ar<-h. f. 

 Physio?., vol. xxiv., 1911) has since shown that the absorption of oxygen by 

 watery lecithin emulsion is greatly increased by the presence of minute traces 

 of iron (1 : 6,000,000). 



2 Mansfeld, "Narkose und Sauerstoffmangel," Pfltiffer't Arc/i., vol. cxxix., 

 1909. 



3 Gregersen, " Untersuchungen iiber den Phosphorstoffwechsel," Zcifw/t. f. 

 physiol. Chfni., vol. Ixxi., 1911. 



vol. xiii., 1912. 



