KIDD'S OWN JOURNAL. 



365 



which concern themselves more particularly 

 with the structure and phenomena of organised 

 beings, the apparatus and agencies set in 

 action by and concomitant with life. Now 

 one of the most obvious microscopic distinc- 

 tions between the organic and inorganic 

 kingdoms, is, the presence of the cell in the 

 former; and yet, in some fossils, for instance, 

 it is by no means easy to detect the cell, 

 whilst, on the other hand, inorganic matters 

 sometimes assume the cellular form. Here 

 then again we fail. 



If we try the value of another distinction 

 adopted by naturalists, even subsequent to 

 the introduction of the microscope, that 

 plants are fixed whilst animals move, we 

 shall find ourselves still at sea; since this 

 distinction is quite inapplicable to many 

 organisms, known only through microscopic 

 agency. Recent researches show that the 

 motile tissues in animals are composed of the 

 same substance found to be present in the 

 cells of all plants ; and which, under the 

 names of nucleus, cytoblast, primordial 

 utricle, and endoplast, has been recognised 

 by all vegetable physiologists. This protein 

 substance is as actively motile in the plant 

 as in the animals : it gives motility to the 

 cells of Protococcus, the fibres of Oscillaria, 

 the spores of many conferva; and fungi, and 

 probably to all the motions observed amongst 

 plants. 



The agents of motion in Infusoria, and 

 upon the internal organs of higher animals, 

 were found to be cilia ; and these organs were 

 pounced upon as the long-wished-for dis- 

 tinctive characteristic of animal life. But 

 they are now known to be present in the 

 zoospores of various confervas, and in the 

 active agents of motion in the Volvox globator, 

 of whose vegetable nature there is little 

 question. The existence of what are called 

 eye-spots was chosen as decisive of animal 

 or vegetable. This test was, in its turn, 

 rejected ; since they are found in both kinds 

 of organism. The Aristotelean definition, 

 "animals possess a mouth," has been re- 

 vived ; and of all merely structural defini- 

 tions, this is the one best suited for the 

 purposes of the naturalist. But this must be 

 taken with limitations, since certain classes 

 of low animal organisms, such as the Fora- 

 minifera, possess no permanent mouth ; 

 although some of them have the power of 

 forming a temporary sac for the purposes of 

 digestion. 



Chemistry endeavored to aid the naturalist, 

 and pointed to cellulose as distinctive of the 

 vegetable. But cellulose has been detected 

 in the Ascidian mollusks, the Acaridce, and 

 in the brain and spleen of man. Chlorophyll, 

 the green coloring-matter of plants, was in 

 its turn proposed as their characteristic, till 

 it was found to be present in several of the 



lower forms of animal life. Starch is a sub- 

 stance constantly present in the plant ; but 

 starch has been found in the brain of man, 

 and is now supposed to be very generally 

 present in the animal kingdom. 



It is thus seen that, whether we look to 

 structure or to chemical composition, both 

 alike fail us in furnishing a distinctive charac- 

 teristic of either division of beings. But, 

 when viewed as a whole, there is neverthe- 

 less a great antagonism exhibited by the 

 animal and vegetable kingdoms. They are 

 mutually dependent, attain the same ends in 

 their growth and organisation, but by con- 

 trary means. The one great function of the 

 animal tissues is the- absorption of oxygen, 

 and the liberation of carbonic acid gas. The 

 great function of the vegetable tissues is to 

 absorb carbonic acid gas, and to liberate 

 oxygen. True it is that, under certain con- 

 ditions, these functions are reversed ; but 

 these departures from their distinctive 

 functions are deviations in appearance only ; 

 they are not real exceptions to these laws of 

 their being, but are due to agencies extrinsic 

 to the essential functions of the plant or 

 the animal. 



Thus, plants exhale carbonic acid at night, 

 and during germination and fructification ; 

 in the first case, however, the gas exhaled is 

 simply that observed during the day, and not 

 decomposed by sunlight ; whilst in the two 

 latter, the emission of this gas is dependent 

 on local causes, changes in the contents of 

 the cells, altogether independent of the life 

 of the plant. The germ, during the growth 

 of its ceils, absorbs carbonic acid and liber- 

 ated oxygen gas, as in the growth of all other 

 vegetable cells. The development of carbonic 

 acid in the plant, arises from the decom- 

 position of the starch and the sugar of the 

 albumen of the seed. The liberation of 

 oxygen by animals is at best doubtful, since 

 in the alleged instances, it is by no means 

 certain but that plants were present, or even 

 mistaken for animals. 



If a series of vegetable compounds be ex- 

 amined, we shall find that they are all capa- 

 ble of being formed out of carbonic acid and 

 water ; in some cases adding ammonia, by 

 abstracting oxygen from the acid and the 

 water. There are one or two seeming 

 exceptions to this rule ; but these are capable 

 of explanation without disturbing it. 



These three compounds, out of which the 

 plant is formed — viz., carbonic acid, water, 

 and ammonia, are all compounds produced 

 by the animals. There is no evidence extant 

 of the animal appropriating and forming 

 organic substances from these three com- 

 pounds. As the assimilation of these three 

 compounds is the distinctive feature of 

 vegetable life, and the liberation of oxygen 

 gas its most constant result ; so, the appro- 



