&:.*: * c i . .;: INTRODUCTION. 



in that they show the formation of formaldehyde in the photolytic 

 decomposition of moist carbonic acid in the presence of chlorophyll. 

 These investigations also do not seem to be entirely free from exception. 

 The conception as to the formation of sugar from formaldehyde is also 

 often different from that explained by v. BAEYER'S idea, and his view as to 

 the assimilation of carbonic acid constitutes a hypothesis which requires 

 further proof. The essentials of this hypothesis, namely, a formation of 

 formaldehyde with a subsequent sugar formation by condensation of the 

 aldehyde groups, is still very generally accepted as probably correct. 

 Independent of the ways and means of how the assimilation processes 

 in the plants originate, it is obvious that the free, radiant? energy of 

 the sun is hereby bound and stored in a new form, as chemical energy, 

 in the combinations formed by the syntheses. 



In animal life the conditions are not the same. Animals are dependent 

 either directly, as the herbivora, or indirectly, as the carnivora, upon 

 plant-life, from which they drive the three chief groups of organic 

 nutritive matter proteins, carbohydrates, and fats. These bodies, 

 of which the protein substances and fats form the chief mass of the animal 

 body, undergo within the animal organism a cleavage and oxidation, 

 and yield as final products exactly the above-mentioned chief components 

 in the nutrition of plants, namely, carbon dioxide, water, and ammonia 

 derivatives, which are rich in oxygen and have little energy. The chem- 

 ical energy, which is partly represented by the free oxygen and partly 

 stored up in the above-mentioned more complex chemical compounds, 

 is transformed into other forms of energy, principally heat and mechanical 

 work. While in the plant we find chiefly reduction processes and syn- 

 theses, which by the introduction of energy from without produce 

 complex compounds having a greater content of energy, we find in the 

 animal body the reverse of this, namely, cleavage and oxidation processes, 

 which, as we used to state, convert chemical tension into living force. 



This difference between animals and plants must not be overrated, 

 nor must we consider that there exists a sharp boundary line between 

 the two. This is not the case. There are not only lower plants, free from 

 chlorophyll, which in regard to chemical processes represent intermediate 

 steps between higher plants and animals, but the difference existing 

 between the higher .plants and animals is more of a quantitative than of a 

 qualitative kind. Plants require oxygen as peremptorily as do animals. 

 Like the animal, the plant also, in the dark and by means of those parts 

 which are free from chlorophyll, takes up oxygen and eliminates car- 

 bon dioxide, while in the light the oxidation processes going on in the 

 green parts are overshadowed or hidden beneath the more intense reduc- 

 tion processes. As in the animal, we also find a heat production in fer- 

 mentation produced by plant organisms ; and even in a few of the higher 



