SECT. 8] CARBOHYDRATE METABOLISM 1023 



liver before the stage of 23 cm. length, i.e. until the iioth day of 

 development. Exactly analogous results were obtained by Zaretzki 

 on the guinea-pig, from the liver of which no glycogen could be 

 isolated till late in development. 



Not until 1908, however, was the assumption of the glycogenic 

 function by the liver put on a firm chemical basis. In that year 

 Lochhead & Cramer made a very complete study of the movements 

 of glycogen in the placenta and foetal liver of the rabbit. 



It may be said at once that it led to a remarkable vindication 

 of the views of Claude Bernard. Lochhead & Cramer appHed the 

 Pfliiger method for glycogen to the embryos and placentas of rabbits. 

 The maternal placenta of the rabbit can be divided into the fol- 

 lowing three parts : (a) that next the uterine muscle, which represents 

 the plane of separation at the end of gestation, (b) an intermediate 

 part, the region of the uterine sinuses, and (c) a part which extends 

 up as a series of peninsulae between the foetal columns, which are 

 analogous to the villi of the human placenta and were described 

 by Chipman as ectodermic tubules with a plasmodial covering. 

 Chipman found histochemically that there was a good deal of gly- 

 cogen still left in (a) at the time of birth, but none in the zone of 

 uterine sinuses and none in the region of peninsular projections, 

 although both these were full of glycogen earlier. When the two 

 parts of the placenta are pulled apart, the delicate peninsulae are 

 left attached to the foetal placenta, so that the glycogen in the foetal 

 part is really not foetal, but maternal. Thus by analysing the two 

 parts of the placenta obtained by mechanical separation information 

 was gained on the changes in glycogen of the two different parts of 

 the maternal placenta. Lochhead & Cramer called the glycogen 

 in the part of the placenta nearest the uterine wall the "distal 

 glycogen", and that in the peninsulae and foetal placenta the 

 "proximal glycogen". This latter portion would come principally 

 from maternal tissue, though a small quota might be supplied from 

 the true foetal part of the placenta. The percentage of distal glycogen 

 they found to be quite comparable to that in the healthy adult liver, 

 rising from the 14th day of development to the i8th, remaining constant 

 from the i8th day to the 22nd, and then rapidly falling till birth. This 

 is shown in Fig. 278. The proximal glycogen was very small in amount, 

 reaching at its maximum only 1 1 mgm. per placenta as opposed to 

 the 93 mgm. of the distal glycogen, and did not affect the curve of 



