764 THE RESPIRATION AND [pt. iii 



investigation of differentiation-processes. Referring again to Table 9 1 , 

 it will be found that embryonic tissue has a very considerable lactic 

 acid production in anaerobic conditions, as much as that of the 

 neoplasms, but that it differs from them on the one hand by the 

 efficiency of its aerobic oxidation mechanism (40 times as adequate 

 as that of rat carcinoma), and from adult tissues, on the other hand, 

 because of their feeble anaerobic glycolysis rate. Per hour per 

 milligram wet weight the 4th day embryo can produce anaerobically 

 0-09 mgm. of lactic acid, i.e. 9 per cent, of its weight; this may be 

 set against the performance of frog's muscle (intact and anaerobic) 

 which produced only o-o6 per cent, of its weight when resting, and 

 1-5 per cent, when stimulated. Warburg concluded that the high 

 N.G.R. was a general property of growing tissues, but that the 

 O.G.R. was only high if the growth was unorganised as in neo- 

 plasms, and regarded this as the most important outcome of his 

 work. "Where growth is, glycolysis is ", he said, " and where abnormal 

 growth is there aerobic glycolysis is." As regards the adult tissues he 

 tried, there were one or two difficulties. Those that might be con- 

 sidered stationary, such as liver and kidney, had very low N.G.R.'s 

 and unmeasurably small O.G.R.'s, while those which were not quite 

 rightly termed stationary, such as testis, had slightly higher N.G.R.'s 

 and small O.G.R.'s. But the grey substance of the brain and the 

 retina were found to have quite peculiar characteristics, an enormously 

 high R.R., nearly three times that of the chick embryo, a very high 

 N.G.R. and a high O.G.R. No satisfactory explanation was or is 

 available for this curious state of affairs, but it has its importance for 

 embryological studies, since in the earlier periods of development 

 the brain vesicles and the eyes make up so significant a proportion 

 of the growing body. The possibility that these results might explain 

 some of those obtained by Child and his school must not be forgotten. 

 Subsequently Negelein found quite different results with amphibian 

 retina, and suggested that such a delicate tissue had been giving 

 cytolysis results in the earlier work. But more recent researches by 

 Krebs have confirmed it. 



Finally Warburg, Posener & Negelein gave some interesting data on 

 the subject of ammonia production, glycolysis and tissue respiration. 

 They found that, when the tissues were placed in Ringer solution to 

 which glucose had not been added, notable amounts of ammonia 

 were formed, indicating a combustion of protein substances. They 



