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 non-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 utricle, as this nitrogenous part is called, is the 

 worker of all subsequent changes undergone by the cell, it 



