8i6 BIOPHYSICAL PHENOMENA [pt. iii 



the allantoic fluid is strongly hypotonic to the amniotic fluid, so that 

 the embryo and amnion form a quite isolated system of high osmotic 

 concentration, surrounded by a hypotonic allantois and yolk. In a 

 certain sense, then, the amniotic fluid in the chick might be said to 

 correspond with the perivitelline fluid in the frog embryo. The slight 

 falling off' in the osmotic pressure of the amniotic fluid which 

 Bialascewicz found in the case of the chick, is paralleled by a similar 

 fall in the case of the sheep (Jacque), the cow (Griinbaum), 

 the dog and the rabbit (PoHti), and man (Ubbels). Again, 

 Jacque and Griinbaum found in mammals a rise, not a fall, of 

 osmotic pressure of the allantoic fluid during development. Con- 

 sideration of the mass of literature dealing with the osmotic pressure 

 of the mammalian amniotic fluid, placenta, and foetal blood, will 

 be deferred to the sections specially devoted to those subjects. How- 

 ever, the allantoic liquid in mammals also is always hypotonic to 

 the foetal blood. 



Bialascewicz pointed out that, in the period when the chick embryo 

 was hypotonic to the amniotic fluid, it was not only not losing water, 

 but rather was actually gaining it. His determinations of embryo 

 water-content, however (see Fig. 220), were in a region which has 

 been very little studied (i.e. before the 5th day) and it has been 

 classical to believe that the embryo steadily loses water from the 

 very beginning. As the discussion on p. 871 shows, however, 

 Schmalhausen's data support those of Bialascewicz. The embryo 

 becomes in turn isotonic and hypertonic with respect to the amniotic 

 liquid, the water-content of which is indeed unknown, but must 

 remain uniformly very high compared to the embryo. 



Straub & Hoogerduyn were impressed by the very large difference 

 existing between the osmotic pressures of the yolk (nearly — o-6° A) 

 and the white (about — 0-45° A) atthe timeof laying^. They devoted 

 a long paper to the explanation of this fact, which is certainly re- 

 markable considering how tenuous and fragile the yolk-membrane 

 is. After considering all the possible systems which might be in- 

 volved (Donnan equilibrium, etc.) they made some estimations of 

 the constituents of the yolk and white (see Table 27) and drew 

 up the following: 



^ At room temperature, this difference can be maintained for at least two months, i.e. 

 quite as long as normal viability is retained (Moran). 



