THE ACTIONS OF FORCES ON ORGANIC MATTER. 37 



metamorphosis. Let us contemplate the several groups of 

 facts which point to this conclusion. 



In the last chapter (§ 2) we incidentally noted the extreme 

 instability of nitrogenous compounds in general. We saw 

 that sundry of them are liable to explode on the slightest 

 incentive — sometimes without any apparent cause ; and that 

 of the rest, the great majority are very easily decomposed by 

 heat, and by other substances. We shall perceive much 

 ^significance in this general characteristic, when we join it 

 with the fact, that the substances capable of initiating extensive 

 molecular changes in the manner above described, are all 

 nitrogenous ones. Yeast consists of vegetal cells containing 

 nitrogen, — cells that grow by assimilating the nitrogenous 

 matter contained in wort. Similarly, the " vinegar-plant,'* 

 which so greatly facilitates the formation of acetic acid from 

 alcohol, is a fungoid growth, that is doubtless, like others of 

 its class, rich in nitrogenous compounds. Diastase, by which 

 the transformation of starch into sugar is effected, during 

 the process of malting, is also a nitrogenous body. So too 

 is a substance called synaptase — an albumenous principle 

 contained in almonds, that has the power of working several 

 metamorphoses in the matters associated with it. These 

 nitrogenized compounds, like the rest of their family, are 

 remarkable for the rapidity with which they decompose ; and 

 the extensive changes produced by them in the accompanying 

 oxy-hydro- carbons, are found to vary in their kinds accord- 

 ing as the decompositions of the ferments vary in their 

 stages. We have next to note, as having here a 



meaning for us, the chemical contrasts between those organ- 

 isms which carry on their functions by the help of external 

 forces, and those which carry on their functions by forces 

 evolved from within. If we compare animals and plants, we 

 see that whereas plants, characterized as a class by containing 

 but little nitrogen, are dependent on the solar rays for their 

 vital activities ; animals, the vital activities of which are not 



