194 NUCLEIC ACIDS AND THE NITROGENOUS BASES 



NITROGENOUS BASES DERIVED FROM GUANIDINE. 

 Guanidine 



/NH 2 

 HN = C< 



X NH 2 



is obtained from proteins by the employment of strong oxidizing rea- 

 gents, its presence has also been detected in various vegetable tissues, 

 among others in the sugar-beet. It is a strong base, yielding strongly 

 alkaline solutions of very stable salts with acids. It is uncertain 

 whether or not it occurs in traces in the blood and tissues. Methyl- 

 guanidine 



/NH.CHa 

 HN = C< 



X NH 2 



is, however, a normal constituent of blood, muscular tissues and urine. 



Guanidine and methylguanidine have a very decided physiological 

 action, two hundred milligrammes of methylguanidine being a lethal 

 dose for a guinea-pig. The amount of methylguanidine in the urine is 

 greatly increased by Anaphylactic Shock, but the symptoms of poisoning 

 are nowise similar to those of anaphylactic shock. They consist in 

 fibrillar twitchings of the peripheral muscles and an excitation of the 

 spinal cord resembling in comparatively slight measure that produced 

 by strychnine or by Curare when directly applied to the cord. In 

 larger doses the myoneural junctions are paralyzed in the same way that 

 they are by curare and the spinal centers are depressed. The fibrillar 

 twitchings produced in muscles by small doses of guanidine or methyl- 

 guanidine are suppressed by calcium salts and in this respect as well as 

 in the character of the muscular excitation, the action of small doses 

 of guanidine resembles the action of sodium salts upon nerves and 

 muscles. 



The marked effect of methylguanidine upon neuromuscular tissues 

 is of especial interest because a derivative of methylguanidine, Creatine, 

 or methyl-guanidine-acetic acid: 



/N.CH 3 .CH 2 .COOH 

 HN = C< 



X NH 2 



is the most abundant nitrogenous base in muscular tissues. The per- 

 centage of creatine varies in different muscles, being higher in voluntary 

 (striated) than in involuntary (smooth) muscles. In given muscles 

 the percentage of creatine varies in different species of animals, but is 

 remarkably constant in different individuals of the same species. The 

 following are the percentages of creatine found in the muscle of various 

 animals by Myers and Fine. 



Per cent. 

 Species. of creatine. 



Rabbit 0.52 



Cat 0.45 



Man 0.39 



Dog . a. 37 



