THE NITROGENOUS EXTRACTIVES. 361 



fluid, and is also a constant constituent of the urine. In the vege- 

 table world it does not occur. 



From the observation of St. Johnson that the urinary kreatinin 

 is not identical with the substance, which can be isolated from 

 muscle-tissue, it has been concluded that the former may not be 

 derived from the muscles at all, but may possibly be referable to the 

 kivatin, which is found in other organs of the body and notably in 

 the thvroid gland. Its identity with these kreatinins, however, has 

 not yet been established, nor is there reason to suppose that these 

 forms differ from the common kreatinin of the muscles. However 

 this may be, the kreatins, viz., kreatinins, are essentially specific 

 decomposition-products of muscle-tissue, and are unquestionably 

 derived from the common muscle-albumins. This is suggested by 

 the observation that larger amounts of kreatin and kreatinin can be 

 isolated from muscles that have previously been worked, than from 

 muscles that have been at rest. I have shown, it is true, that the 

 nitrogenous components of the muscle-tissue enter into considera- 

 tion only in a secondary manner, as a source of muscular energy, 

 but this does not preclude the possibility, that during work the 

 metabolism of the muscle-albumins is increased. That such an 

 increase will of necessity become more apparent during starvation is, 

 of course, self-evident, and we find, as a matter of fact, that under 

 such conditions a corresponding increase in the formation of kreatin 

 occurs. 



While our knowledge of the manner in which kreatin and 

 kreatinin are produced in the body is as yet practically nil, we know, 

 on the other hand, that, when once formed, it is further decomposed, 

 and contributes toward the formation of urea. Artificially this can 

 readily be accomplished by boiling kreatin with baryta- water, when 

 it is decomposed with the formation of urea and methyl-glycocoll. 

 At the same time, however, methyl-hydantoin and ammonia result. 

 Whether or not the decomposition of kreatin, which is now known 

 to occur in the muscle-tissue itself, takes place in the same manner, 

 is not known. But if so, we could readily understand why traces 

 of glycocoll are also so constantly met with. Both substances, how- 

 ever, are manifestly removed as rapidly as possible, as neither urea 

 nor glycocoll is ever found in the tissue itself beyond traces. 1 



In this connection it is interesting to note that Guareschi and 

 Mosso have succeeded in extracting methyl-hydantoin also from the 

 muscles of the calf. That methyl-hydantoin belongs to the class of 

 ureids has already been pointed out, and we may therefore assume 

 that the substance is further decomposed with the formation of 

 urea, if further researches should show that the decomposition of 

 kreatin actually takes place in the living tissue also, as outlined 

 above. The small amount of ammonia, which at the same time 



1 This statement requires modification, ns quite considerable amounts of urea 

 can be demonstrated in the muscles of certain fishes, such as the shark and the 

 sturgeon. 



