154 ORGANIC CHANGES. 



sess the singular property of causing substances 

 which do not contain nitrogen to decompose or change 

 likewise. 



355. When vegetable substances, such as lignin or 

 sugar, are burnt in the air, water and carbonic acid 

 are produced ; precisely the same substances are 

 formed by decay, as by combustion. When gluten 

 and albumen are burnt, water, carbonic acid, and 

 ammonia are formed. 



356. The transformation of one organic substance 

 into another, is a very interesting and remarkable 

 operation. It is plain that such changes must be 

 constantly going on in the organs of plants, and 

 hence everything which throws light on the nature 

 of these transformations is of interest. 



357. When the chemical affinity which unites the 

 elements of any compound substance is feeble, and 

 especially when the compound consists of several ele- 

 ments, there is always a considerable tendency to 

 decompose, and the elements are very prone to ar- 

 range themselves in simpler, and more permanent 

 combinations. Very slight circumstances therefore 

 are able to determine the decomposition of such 

 compounds, and the change may be brought about 

 in various ways. 



358. Some of these transformations are spontane- 

 ous, some require the presence of a particular sub- 

 stance, which however has no direct chemical action 

 on the compound itself, or on any of its elements ; 

 and many are induced, or caused by the example of 



