1038 CARBOHYDRATE METABOLISM [pt. hi 



chemically the various regions of the embryo according to the depth 

 of colour obtained with iodine and other reagents. The two most 

 outstanding surveys of this kind are those of Creighton and of 

 Sundberg, in whose papers will be found lists of tissues and organs 

 microscopically rich and poor in glycogen respectively. Creighton 

 introduced the theory that glycogen "acts in the embryo as the pre- 

 cursor or deputy of haemoglobin until such time as the vascularity of 

 the part is sufficiently advanced, and in other cases as the substitute 

 of haemoglobin from first to last, i.e. in those tissues which are 

 built up in whole or in part without the direct access of blood". 

 Creighton also thought that "the cartilages which are destined to 

 continue throughout life as cartilages have little or no glycogen in the 

 foetal period, but those which later will ossify have plenty and it usually 

 appears in the spots which afterwards become ossification centres". 



Nobody now accepts Greighton's views and the attribution of any 

 special embryological importance to glycogen is superfluous. While it 

 may be useful to know the histological distribution of glycogen in the 

 embryo, at present little physico-chemical meaning can be attached 

 to most of this work. Investigators continue to labour along these 

 lines, however, e.g. Ellis; Gragert; Glinka; Gierke; Gage; Lubarsch; 

 Togari; Jordan. Livini has published a series of papers on the glyco- 

 gen distribution in human embryos. None can be demonstrated in 

 the liver till the end of the 2nd month. The muscles, lungs, skeleton 

 and epithelial tissues begin then to acquire it; the pancreas, salivary 

 glands, thyroid, parathyroid, thymus, suprarenal medulla, kidneys, 

 smooth muscles, testes, ovaries, etc., have very little, and it appears 

 irregularly, while the central nervous system, the suprarenal cortex 

 and the retina never have any at all. Livini found that, as the liver 

 glycogen rises towards the end of gestation, it falls in the organs of 

 the second class, so that an additional source, other than the placenta, 

 may be envisaged. All Livini's work is histochemical. It is clear that 

 the glycogen of the body as a whole rises during embryonic life 

 (Murray for the chick, Lochhead & Cramer for the rabbit, Mendel 

 & Leavenworth for the pig, and Aron for the cow and the sheep) . 

 The only contradictory piece of evidence is contained in a dissertation 

 by Kistiakovski, who stated that the quantity of glycogen in embryo 

 cows and sheep diminished gradually until birth. This publication 

 is not available in England, but it can probably be disregarded in 

 view of the consensus of opinion. 



