. Chemical embryology. Embryology. GENERAL METABOLISM [PT. Ill had 82-8 per cent, and the cord 79-0 per cent., while Donaldson found for Rana adult brain 84-9 per cent, and cord 80-5 per cent. Rosenheim, on the other hand, found in human brain 90-29 per cent, for the 36 weeks' foetus and 85-8 per cent, for the infant shortly after birth, and a trend in the same direction was found by Gundobin and by Koch, who obtained the following figures: Brain of foetus of pig 50 mm. long Brain of foetus of pig 100 mm. long Brain of newly-born albino rat ... Brain of adult albino rat 0/ /o 90-78 91-01 89-58
. Chemical embryology. Embryology. GENERAL METABOLISM [PT. Ill had 82-8 per cent, and the cord 79-0 per cent., while Donaldson found for Rana adult brain 84-9 per cent, and cord 80-5 per cent. Rosenheim, on the other hand, found in human brain 90-29 per cent, for the 36 weeks' foetus and 85-8 per cent, for the infant shortly after birth, and a trend in the same direction was found by Gundobin and by Koch, who obtained the following figures: Brain of foetus of pig 50 mm. long Brain of foetus of pig 100 mm. long Brain of newly-born albino rat ... Brain of adult albino rat 0/ /o 90-78 91-01 89-58 78-10. It is safe to say, then, that, though in certain cases the water- content of embryonic tissues seems to remain unchanged with age, there are a few instances of a rise, and the majority of experi- ments show that it falls. The ex- planation of this fall is difficult, though, as we have observed, some investigators have seen in it perhaps the most fundamental attribute of the ageing-process. A point which does not seem to have been noticed so far is that the high water-content in the early stages may be related to the importance of primitive connective tissue and its con- tained lymph. I have already drawn attention to the primi- tive undifferentiated connective tissue, first discovered by von Szily, in connection with the initially high concentration of glucose in combination with protein^, and it will again be mentioned in connection with the relatively high silicon content of young em- bryos. But what is important here is the fact that connective tissue has always a high water-content, and this might explain the pheno- menon now under discussion. Thus Skelton found that bleeding in mammals produced a flow of water from the tissues into the blood, and by appropriate experiments he was able to ascertain what per- ^ See p. 566. o Cowmuscle(jacubovitsch) ® Pig brain (Mendel S^Leavenworth) © Pig liver ( " " " ) o Sheep lung(Faure-Fremieb«tDragoiu) â
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