SECT. 9] PROTEIN METABOLISM 1131 



brain tissue from embryo rats, maintained in vitro with precautions 

 ensuring sterility, and on these they carried out ammonia and urea 

 estimations, making special provision for a complicated series of con- 

 trols necessitated by the autolysis of the medium when held at 37°. 

 Comparing the results from "resting" tissue, i.e. tissue submerged 

 and floating so that it cannot grow but can yet live, with those from 

 tissue attached to cotton-wool fibres and vigorously growing, Holmes 

 & Watchorn found much more urea and ammonia production from 

 the latter than from the former. Unfortunately, it was not usually 

 practicable to weigh the pieces of kidney selected for culture, so that 

 we cannot tell what level of metabolic intensity this represented, but 

 in one instance 33 mgm. wet weight of kidney tissue had produced 

 after a time unstated 0-023 nigm. of urea and 0-039 mgm. of ammonia, 

 or about 0-05 mgm. of total nitrogen, i.e. 0-15 mgm, per 100 mgm. 

 wet weight of the original tissue. Holmes & Watchorn found no 

 evidence for the activity of urease in their cultures. In brain cultures, 

 on the other hand, there was a definite suggestion of the action of 

 urease, and when good growth took place there was found a sur- 

 prising result, namely, that there was a considerable fall in the am- 

 monia and urea nitrogen. Possibly a synthesis of nitrogenous sub- 

 stances such as choline was occurring. In a later paper these 

 investigators added glucose to the medium of culture, and found that 

 it gave rise to a marked alteration in the metabolism of the tissue, 

 bringing about a definite inhibition of ammonia and urea formation. 

 This was the second in vitro demonstration of the protein-sparing 

 action of the carbohydrates: for the first see Warburg, Posener & 

 Negelein (p. 765). Still later, Holmes & Watchorn used their 

 technique to study the relation of cyanate, hydantoinacetic acid, etc., 

 to urea and ammonia production by embryonic kidney cells in vitro. 

 As regards the nourishment of the mammalian egg-cell before its 

 implantation into the uterine wall, Emrys-Roberts suggested that the 

 secretion of the mammalian uterus was analogous to that of the avian 

 oviduct, and supplied a kind of egg-white which the ovum could 

 digest and dissolve. He made no experiments to prove the point, 

 but he conceived that the gelatinous envelope which surrounds the 

 embryo of the rabbit and the mole before implantation was produced 

 by a fermentative and coagulating action on the part of the tropho- 

 blast. Sobotta and Gaffier have produced evidence in favour of such 

 a mechanism. 



