782 BIOPHYSICAI, PHENOMENA [pt. rii 



unfertilised ovarial Petromyzon eggs. Bataillon's data on Ascaris eggs 

 might be treated in a similar way. 



Later, Backmann, Sundberg & Jansson studied the effect of 

 excess and lack of oxygen on the osmotic pressure curve during 

 embryonic and larval life in the frog. Their results (which were 

 never reported in full) are shown on Fig. 177. Development 

 in almost pure oxygen led to a precocious augmentation of the 

 osmotic pressure rise. They did not state, however, whether de- 

 velopment in almost pure oxygen led to any shortening of the 

 hatching time, or to more rapid differentiation or growth. Lack 

 of oxygen was produced by causing the eggs to develop in water 

 covered by a thick layer of paraffin oil. In such circumstances, 

 the osmotic pressure of the eggs followed the usual course, 

 until at about the 5th day the rise began to cease, and the gas- 

 trulae died shortly afterwards with an osmotic pressure of from 

 A — 0-09° to A — 0-055°^. The membranes seemed to lose their 

 elasticity from the 3rd day onwards, and there was great swelling. 

 Unfertilised eggs placed under similar conditions cytolysed after only 

 24 hours, their osmotic pressure having fallen to isotonicity with the 

 pond water. Backmann went on to study the effects of temperature. 

 Kept at 30 to 40° the eggs swelled a good deal, but in spite of that 

 they had an osmotic pressure by the 3rd day which was up to normal, 

 or a little above it (A — 0-048 at 40° and A — 0-040 at 30°). Kept at 

 5 to 6° the development was much retarded, and the rise in osmotic 

 pressure, though at first behaving quite normally, was in its second 

 phase much drawn out. Thus on the 21st day the eggs at the low 

 temperature would have a A of — 0-30°, while eggs at normal 

 temperature (17°) would have — 0-39°, and eggs at normal tempera- 

 ture but of the same morphological stage as the cold ones would 

 have — 0-25°. Backmann concluded that all these experiments 

 showed a close association between morphological development and 

 osmotic pressure, the latter entity being unable to vary more than 

 a little independently of the former. As the temperature coefficient 

 for osmotic pressure is exceedingly small, that entity must be dependent 

 in its turn on some process with a marked temperature coefficient, 

 i.e. whatever reaction or reactions were controlling the growth-process 

 as a whole (see also on this p. 910). 



1 Thus lack of oxygen abolishes the mechanism which maintains the osmotic pressure 

 difference, but the parallel with the vitelline membrane of the hen's egg is not close for 

 here the embryonic development is affected too (see p. 817). 



