1098 



PROTEIN METABOLISM 



[PT. Ill 



A good deal of light has been thrown on the functioning of the 

 embryonic excretory organs in the chick by the injection of vital 

 dyes into the egg during development. The pioneer in this line of 

 work was Bakounine, who in 1895 injected indigo-carmine intra- 

 venously into chick embryos varying from 3 to 1 5 days' development, 

 and in all cases observed the dye in the cells of the proximal portion 

 of the mesonephric tubules. Undoubtedly excretion of the stain was 

 occurring. Zaretzki was the first to inject dyes into the air-space. 

 He used trypan blue, trypan red, neutral red, methylene blue, 

 fluorescein, eosin and ethyl green. 

 With trypan blue there was in the 

 late stages of incubation a slight 

 colouring of the amniotic liquid, 

 but not of the embryo. When the 

 dye was injected into the outer | 

 wall of the allantois, he observed 

 a diffuse staining of the embryo, 

 amniotic liquid and foetal mem- 

 branes. These results were rather 

 difficult to interpret, as were those 

 later obtained by Graper, who 

 unsuccessfully tried to use an in 

 vitro technique for keeping stained 

 whole blastoderms alive outside 

 the egg. Hanan has shown more 

 recently that trypan blue, once 

 within the circulation of the em- 

 bryo, is excreted through the kidneys, and appears in the allantoic but 

 not in the amniotic liquid, strongly suggesting that, in the case of birds, 

 foetal urinary water does not contribute to the formation of the latter. 

 The excretory activity of the mesonephros, he found, began on the 

 4th day of incubation, which agrees very well with the earlier results 

 of Bakounine and of Wislocki, and with the fact established by Boyden 

 that hydronephrosis cannot easily be produced before the 4th day. The 

 more recent researches of Atwell & Hanan and of Hurd with trypan 

 blue have established (if the behaviour of the dye in the cells is any 

 criterion) that the excretory activity of the mesonephros begins on 

 the 4th day, and goes on alone till the 1 1 th day, at which time the 

 metanephros comes into operation. Both function together till the 



b- 

 ZQ. 



Fig. 333. 



