Minute Organisms. 105 



Another reason for considering them animals, he states to be, " that 

 whereas plants require for their growth the hght of the sun — in 

 fact, their very growth is a process of absorption of heat by their 

 leaves from the rays of the sun — and plants by so doing render heat 

 latent, as we sometimes express it, that is, they caase an apparent 

 disappearance of heat, and lower the temperature of smTounding 

 space ; animals, on the contrary, give off heat during the exercise 

 of their vital functions, and do not need to be exposed to heat or to 

 continuous light for their growth," This is surely an astonishing pas- 

 sage, and physiologists will feel compelled to demur to the assertion 

 that heat is not necessary to the performance of the vital functions 

 of animals, and that animals in general could hve without light. If 

 animals gave out all the heat they wanted, by their own processes, we 

 might in this cool chmate simphfy clothing, abandon the domestic 

 winter fire, and never have om* benevolent sentiments shocked by 

 tales of fellow-creatures frozen to death. It is certainly an error 

 to say that " animals do not need to be exposed to heat," and also 

 to represent plants as simply heat consumers, and not also heat pro- 

 ducers. Mr. Grove, in his ' Correlation of Physical Forces,' says, 

 *' Heat is an immediate product of chemical affinity. I know of 

 no exception to the general proposition, that all bodies in chemically 

 combining produce heat." It is from this general law that plants 

 do evolve heat in their processes of combination, and at times they 

 evolve enough to produce a striking elevation of temperature, as is 

 well known. It cannot be affirmed of all fungi, acting as ferments, 

 that they feed upon complicated substances, though some do ; and 

 on the other hand, the food of other plants is not at all times, and 

 always simple. For example, in the last edition of Dr. Carpenter's 

 ' Principles of Human Physiology,' edited by Mr. Power, I find an 

 allusion thus made to a paper by Eisler, " On the Absorption of 

 Humus by Plants," and on the functions of ordinary plants as com- 

 pared with those of Fungi: — "The exhalation of carbonic acid is not 

 peculiar to fungi or germinating embryos, for it takes place during 

 the whole life of flowering plants, both by day and by night, in sun- 

 shine and in shade, and from their green as well as from their dark 

 surfaces. And it is not improbable that, as in the case of fungi, its 

 source lies partly in the organic matters absorbed ; recent investiga- 

 tions having rendered it probable that plants really take up and 

 assimilate soluble humus." Now soluble humus is a highly complex 

 •substance, probably consisting of various acids and ammonia, and 

 requiring to part with some of its carbon to fonn the normal con- 

 stituents of plants. 



It is often a matter of interest to the microscopist to say whether 

 organisms, occupying a sort of border-land, belong to the animal 

 or the vegetable kingdom, and in many cases this cannot be done 

 with precision or certainty. Some remarks of Boussingault will 



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