298 TRANSACTIONS OP SECTION I. 



In the protein of ox-flesh it occurs to the extent of about 7 to 11 per cent., so 

 that taking the protein of muscle at 20 per cent., there is present in ox-flesh 

 some 2 per cent, of arginin. This contains about 40 per cent, of guanidin, so 

 that in the arginin alone there is no less than 0-8 per cent, of combined 

 guanidin and 5-07 per cent, guanidin nitrogen, or, taking the total nitrogen of 

 flesh at 3-7 per cent., some 15 per cent, of the total nitrogen, or on the lower 

 analysis about 11 per cent. 



From cat's muscle Miss Henderson ^ recovered an average of 0-56 per cent, 

 of total guanidin, i.e., 0-4 per cent, guanidin nitrogen, with 3-7 per cent, of 

 total nitrogen in the muscle. The guanidin nitrogen amounted to nearly 10-4 per 

 cent, of the total nitrogen. 



3. Specific Action of Constituents of Proteins. 



An important aspect of the metabolism of proteins is the physiological 

 activity of some of their products of disintegration. 



Their specific dynamic action in stimulating the rate of metabolism and 

 increasing heat production, first demonstrated by Rubner, has been shown by 

 Lusk to be due to the action of their constituent amino acids. 



Some of Mansfield's work strongly suggests that this action may be con- 

 trolled by the thyroid gland, but into this question it is impossible to enter at 

 present. 



The possible importance of one product of disintegration of protein, the 

 guanidin moiety of the arginin molecule, has so far received no attention. 



i. Sources. 



Its real significance has been too readily ignored on account of the demonstra- 

 tion of the formation of urea in the metabolism of arginin. But while Kossel 

 and Dakin ^ showed that this urea formation goes on in the liver, they did not 

 find the same evidence of the change in muscle. Thompson, 'i after the adminis- 

 tration of arginin by the mouth and subcutaneously to dogs, recovered very 

 varying amounts in the form of urea and got a marked increase in the excretion 

 of ammonia. He was forced to conclude that arginin stimulates nitrogenous 

 metabolism, in this way acting as the more recent work of Lusk has shown that 

 so many amino acids act, and rendering any conclusion as regards the complete 

 conversion to urea impossible. 



More recently Inouye,^ in perfusion experiments through the liver and in 

 autolysis experiments, has observed an increase in creatinin after the addition 

 of arginin. 



Thompson,^ shortly before his tragic and untimely death, published a series 

 of experiments which proved fairly conclusively that arginin alone, and still more 

 markedly when given along with methyl citrate, distinctly increases the output 

 of total creatinin, mainly by increasing the output of creatin. 



In the face of such experiments it must be concluded that a certain part at 

 least of the guanidin moiety of arginin escapes conversion into urea and 

 ultimately forms creatin. 



That the guanidin in arginin, creatin and other substances may be primarily 

 formed from non-guanidin nitrogen was demonstrated by Burns ' in the develop- 

 ing chick. He found that the amount of guanidin in the egg showed a steady 

 increase to the twelfth day of incubation and only after this date did creatin 

 appear. In considering the possible origin of the guanidin thus formed, one is 

 almost forced to look to the cholin part of the lecithin molecule as the only 

 possible source. The formation of guanidin or at least of creatin, methyl- 

 guanidin acetic acid, from cholin is not purely hypothetical, for Riesser * has 

 not only considered it on theoretical lines — that it can be produced by a union 

 of oholin with urea — but he has actually adduced evidence to show that in 

 rabbits the creatin of muscle is increased after administration of cholin. 



Baumann, Hines and Marker ' in a short note state that by perfusing with 

 choline and urea in the dog, they got an increase of the creatin in muscle. 



If cyanamid instead of urea took part in the reaction methyl-guanidin misfht 

 be directly formed, the ethyl group of the cholin being oxidised away and two 

 methyls removed. 



