196 THE PHYSIOLOGY OF REPRODUCTION 



times that of the same quantity of untreated eggs. The heat 

 production was increased from 0'9 gram-calorie per hour to 3'4 gram- 

 calories per hour, after treatment with valerianic acid by which 

 artificial membrane formation was induced. 



A great many of Loeb's and Warburg's experiments point con- 

 clusively to the cortical layer of the egg and the egg-membrane as 

 being the controlling factors in the oxidation processes of the egg. 

 Any change brought about in these is immediately reflected in the 

 oxygen uptake of the egg. Loeb has, of course, based his method of 

 producing artificial parthenogenesis on the fact that alteration of the 

 surface layer of the egg renders the commencement of development 

 possible. But how can the cytolytic destruction of the surface layer 

 of the egg lead to development ? Warburg has shown that there 

 are good reasons for believing that the oxidations taking place 

 in the egg occur mainly at its surface, for NaOH, which does 

 not diffuse into the egg, raises the rate of oxidations more than 

 NH 4 OH, which readily diffuses into the egg. 



Moreover, he found 1 that the addition of iron salts to the broken- 

 up eggs, or acetone egg powder, was followed by a considerable increase 

 in the oxygen consumption of these egg preparations, and he found 

 marked traces of iron in the sea-urchin egg. He suggests that the 

 iron probably acts the part of a catalyser. If the iron were located 

 in the lipoid layer of the egg in a condition in which it was unable to 

 act, some slight alteration in this layer, due to the action of the 

 sperm, might render it active or bring both the iron and the oxidisable 

 substrate into a condition in which they could quickly interact. We 

 know from Thunberg's work 2 that lecithin in a watery suspension 

 consumes considerable oxygen in the presence of iron salts. The egg 

 of the sea-urchin contains considerable quantities of this lipoid. 



Warburg has pointed out that there are many respects in which 

 the metabolism of the fertilised egg resembles that of the yeast-cell. 

 In each it has been shown that structure plays a very important 

 part, as both acetone preparations of the egg and the yeast-cell 

 retain considerable respiratory power. Meyerhof 3 finds, however, 

 that if acetone yeast is well washed with water, it soon loses its 

 capacity to take up oxygen. If a little watery extract of yeast is 

 added to the washed yeast it immediately regains its lost respiratory 

 power. In the water used in washing the yeast Meyerhof found the 



1 Warburg, " Uber die Rolle des Eisens in der Atmung des Seeigeleis- 

 nebst Bemerkungen iiber einige durch Eisen beschleunigten Oxydationen," 

 Zeitsch. P/iysiol. Ckem., vol. xcii., 1914. 



2 Thunberg, " Untersuchungen iiber autoxydable Substanzen und autoxy- 

 dable Syateme von physiologischen Interesse," Skand. Arch. Physiol., vol. 

 xxiv., 1911. 



3 Meyerhof, "Untersuchungen zur Atmung getoteter Zellen," Archiv. f. 

 ges. Physiol., vol. clxx., 1918. 



