ALKALOIDS CONTAINING OXYGEN. 133 



ALKALOIDS CONTAINING OXYGEN. 



Few substances of this group belong to zoo-chemistry ; but 

 they are more important in reference to physiological chemistry 

 than the non-oxygenous alkaloids which we have just considered, as 

 they have either been found preformed in the animal body, or are 

 able to throw considerable light on the constitution of the sub- 

 stances yielding them, and on organic chemistry generally. We 

 shall therefore only consider in any detail the following substances, 

 viz. : creatine, creatinine, tyrosine, leucine, sarcosine, glycine, 

 (glycocoll) urea, guanine, xanthine, taurine, and cystine ; and here 

 it will be necessary to obtain some acquaintance with the general 

 chemical relations of all these bodies before we enter upon the con- 

 sideration of each individually. 



The oxygenous alkaloids do not yield in respect to their basicity 

 to those containing no oxygen ; for many of these bodies not only 

 separate the oxides of the heavy metals from their salts but also 

 liberate ammonia. Their basicity, however, exhibits such gradual 

 differences that no accurate line of demarcation can be drawn 

 between decidedly basic and indifferent nitrogenous bodies. Thus 

 leucine and creatine are perfectly indifferent bodies, while sar- 

 cosine, which is homologous to leucine, and creatinine, which is so 

 similar to creatine, are strongly basic; but as these indifferent 

 bodies present a close theoretical relation to the basic bodies, or 

 actually possess weak basic properties, we do not think that it is 

 expedient to separate them. 



There is no direct ratio between the saturating capacity of these 

 bodies and the quantity of oxygen or even of nitrogen that they 

 contain, for in creatinine, for instance, only the third part of the 

 nitrogen contained in the body corresponds to the saturating capa- 

 city, while in xanthine it is the fourth, and in guanine only the fifth 

 part. In these bodies the nitrogen may be similarly incorporated 

 with other elements as an adjunct of the base ; thus we have seen 

 that nitrogen may be artificially added to aniline under the form of 

 cyanogen or hyponitric acid, and that harmaline (from Peganum 

 harmala) takes up hydrocyanic acid without changing its saturating 

 capacity. 



The greater number of the alkaloids containing oxygen are 

 crystallisable ; none are fluid at an ordinary temperature ; the ma- 

 jority have a more or less bitter taste ; not being volatile, they have 



