38 THE DATA OF BIOLOGY. 



thus dependent, mainly consist of nitrogenous substances. 

 There is one marked exception to this broad distinction, how- 

 ever; and this exception is specially instructive. Among 

 plants, there is a considerable group — the Fungi — many mem- 

 bers of which, if not all, can live and grow in the dark ; and 

 it is their peculiarity that they are very much more nitro- 

 genous than other plants. Yet a third class of facts 

 of like significance, is disclosed when we compare different 

 portions of the same organisms. The seed of a plant contains 

 nitrogenous substance in a far higher ratio than the rest of 

 the plant ; and the seed differs^ from the rest of the plant in 

 its ability to initiate, in the absence of light, extensive vital 

 changes — the changes constituting germination. Similarly 

 in the bodies of animals, those parts which carry on active 

 functions are nitrogenous ; while parts that are non-nitro- 

 genous — as the deposits of fat — carry on no active functions. 

 And we even find that the appearance of non-nitrogenous 

 matter, throughout tissues normally composed almost wholly 

 of nitrogenous matter, is accompanied by loss of activity : 

 what is called fatty degeneration, being the concomitant of 

 failing vitality. One more fact which serves to make 

 still clearer the meaning of the foregoing ones, still remains — 

 the fact, namely, that in no part of any organism where vital 

 changes are going on, is nitrogenous matter wholly absent. 

 It is common to speak of plants — or at least all parts of 

 plants but the seeds — as lion-nitrogenous. But they are only 

 relatively so ; not absolutely. The quantity of albumenoid 

 substance contained in the tissues of plants, is extremely small 

 compared with the quantity contained in the tissues of ani- 

 mals ; but all plant-tissues which are discharging active 

 functions, contain some albumenoid substance. In every 

 living vegetal cell there is a certain part that contains nitro- 

 gen. This part initiates those changes which constitute the 

 development of the cell. And if it cannot be said that the 

 primordial tttride^ as this nitrogenous part is called, is the 

 worker of all subsequent changes undergone by the cell, it 



