ALBUMENOID SUBSTANCES. 79 



As oxygen therefore is essential to their growth, its presence is also 

 necessary for putrefaction. Furthermore, as no plants can grow with- 

 out moisture, and as they require a temperature of moderate warmth, 

 putrefaction must also be suspended both by desiccation and by exces- 

 sive cold or heat. 



Fermentation and putrefaction, accordingly, are analogous processes, 

 going on under the influence of different microscopic vegetations. The 

 former takes place in saccharine liquids, the latter in those containing 

 albumenoid matter ; since the yeast-plant requires for its growth a pre- 

 ponderance of carbo-hydrates, while bacterium cells are nourished by 

 the absorption of nitrogenous matter. 



Origin of the Albumenoid Substances. Albumenoid matters are 

 first produced in the vegetable world by assimilation of nitrogen with 

 the carbo-hydrates. This is proved by the fact that green plants which 

 can produce starch and sugar from carbonic acid and water, if supplied 

 with moisture containing nitrogenous salts, will thrive vigorously and 

 increase many fold their contents of albuminous matter.* The pro- 

 duction of this new material will take place in other parts of the plant 

 beside the leaves, provided there be present saccharine juices already 

 formed and nitrogen compounds fit for absorption. Furthermore, color- 

 less plants, which cannot produce starch or sugar for themselves, if 

 nourished with saccharine solutions and inorganic nitrogen compounds, 

 will also largely increase the mass of their albumenoid ingredients. 



It appears that the nitrogen thus assimilated by plants is not absorbed 

 in a free state. Notwithstanding the abundant quantity of this element 

 in the air, it is accepted by vegetable physiologists, as the result of 

 decisive investigations, that the free atmospheric nitrogen is not avail- 

 able for vegetation, f Plants appropriate their nitrogen, both from the 

 atmosphere and the soil, in the form of nitrates and ammonium salts, 

 which are absorbed by the roots, taken up by the vegetable juices, and 

 thus serve for the production of albumenoid substances. The sulphur 

 requisite for these matters is taken up in the form of sulphates, which 

 are afterward decomposed in the vegetable juices. 



Classification of the Albumenoid Substances. The arrangement of 

 these matters in groups, according to appropriate generic characters, is 

 necessary to facilitate their study and description. Attempts at such 

 a classification, based upon their intimate chemical structure, must be 

 futile, so long as we are destitute of certain knowledge in this respect. 

 Even their characters of solubility in water, dilute acids or alkalies, or 

 saline solutions, vary in different cases by such slight gradations that 

 they can only be considered as convenient methods of diagnosis rather 

 than as positive distinctions. Their treatment by stronger reagents 

 yields substances which may be of interest for theoretical chemistry, 

 but which are not to be found in the living body, and have no physio- 



* Mayer, Lehrbuch der Agrikultur-Chemie, Heidelberg, 1871, Band i. pp. 145, 150. 

 f Hoppe-Seyler, Physiologische Chemie. Berlin, 1877, p. 48. 



