Atkins — Osmotic Pressures of the Blood and Eggs of Birds. 129 



sodium salt, viz. 0'473 per cent., would give a value A = 0-282" C, leaving 

 0-292° C. as the depression produced by the organic solids and the remainder 

 of the inorganic. In the egg the sodium chloride amounts to 0-148 per cent., 

 which produces a depression A = 0-091° C, leaving 0'361°0. as due to the 

 organic and remaining salts, so the egg is richer than the blood in organic 

 crystalloids. These values of A were got by interpolation from the results of 

 Loomis ;' as his observations are very close together, iaterpolatiou introduces 

 no error. 



Considering, now, the difference between the values of A for serum and 

 egg As - Ae = 0'122°O. ; the difference in the sodium chloride depressions 

 gives AsNac' - AeNaCi = 0-191° 0. Thus the loss of chlorides is more 

 than sufficient to account for the difference in the values of A for blood and 

 eggs. This is using the mean values in the calculations. 



But taking the maximum values of A for serum and the minimum value 

 for egg, As - Ae = 0'171°O. ; while the minimum amount of sodium chloride 

 in the serum and the maximum amount in the egg give AsNaCi - AeNaCi 

 = 0'158°C., thus reversing the result. On the whole, it appears probable 

 that there is in the egg a reduction in the inorganic salts beyond what is 

 required to account for the difference in A given by serum and egg, the 

 excess depletion being compensated by an increase in the organic crystal- 

 loids. I hope, liowever, to investigate this point further. 



This reduction in pressure accounted for above may take place either — 



(ff) in the ovary, 



[b) during the passage of the egg down the oviduct, or 



(c) in both stages. 



Consider now the first case — («). The ovum is being enlarged by the 

 deposition of nutrient substances, resulting in a giant cell composed almost 

 entirely of metaplasm. It is hard to see why tliere should be any reduction 

 in pressure under these conditions ; so it seems probable that the osmotic 

 pressure of the ovum in the ovary is the same as that of the surrounding 

 body-cells. 



[h) When the ovum begins to travel down the oviduct, it is coated with 

 various layers of albumen secreted by the glands of the duct. Now these 

 secretions may have a low osmotic pressure, like human saliva, which freezes 

 at - 0-10° C, while human blood freezes at - 0-56° C. Diffusion taking place 

 between tlie yolk and the albuminous coating would soon equalize the concen- 

 tration, so there would be a slow fall in the freezing-point of the yolk, 

 from that of the blood to tliat of the egg as determined when laid. This 



' Wieden. Aimal. 31, 1894, s. 515. 



