44 MANUAL OF HISTOLOGY. 



calculi ; it has, however, been since found to occur very extensively, but 

 in small quantities, in many different organs in the brain, in glands and 

 muscles, and in the urine. 



Allantoin, C 4 H 6 N 4 3 . 



This compound crystallises in glittering, colourless prisms, of rhombic 

 fundamental form (fig. 25). It is difficult of solution in cold, but more 

 soluble in warm water ; not at all so in ether, on the contrary. Allantoin 

 appears neutral, but combines with metallic oxides. Through the agency 



of yeast-cells it may be split up 

 into ammoniacal salts and urea. 



Allantoin may be obtained with 

 urea artificially on the oxidation 

 of uric acid, by boiling with super- 

 oxide of lead. 



It is a constituent of the allan- 



urine of young calves. According 

 to Frericlis and Staedeler, it ap- 

 pears in the urine of mammals, 

 coincident with disturbance of 

 their respiratory functions, but 



Fie. 25. Crystals of allantoin ,-, 



whether in man under similar 

 circumstances has not yet been decided. 



It must be regarded, like the bases with which it is physiologically 

 related, as a decomposition product of azotised substances in the body. 



30 - 



Kreatin, C 4 H 9 N 3 O a + H 2 O . 



This compound, known even before its constitution was accurately 

 ascertained by Liebig, is of neutral reaction. It is soluble, in a minor 

 degree, in cold, more so in hot water, arid quite insoluble in pure alcohol 

 and ether. It crystallizes in transparent rhombic prisms ^fig. 26), loses 



its water of crystallization at 100 C., and at 

 a higher temperature melts with decomposi- 

 tion. With acids kreatin forms salts of acid 

 reaction. 



Some of the decomposition products of 

 kreatin are also of importance. Dissolved in 

 acid and heated, it is transformed, with the 

 loss of one molecule of water, into a closely- 

 related substance, which also occurs naturally 

 in the body; this is known as kreatinin, 

 C,H.KO. Boiled with baryta water, kreatin 



Fig. 26. Crystals of kreatin. 4 7 3 . , i-r' -KT /^ /!' i_ 



passes into urea, CH 4 N 2 O (taking up a mole- 

 cule of water), and another base, not yet met with naturally, known as 

 sarkosin (methylglycocoll), C 2 H 4 (CH 3 )JST0 2 . 



Kreatin springs, according to Volkard, from sarkosin and cyanamid = 



This is looked upon as methyluramido-acetic acid (methylguanidiii- 

 acetic acid). 



