NATTJKAL science news. 



163 



What is an Animal? 



The title of this paper may 

 sound somewhat paradoxical in 

 the ears of not a few readers; and 

 this for the simple reason that the 

 ordinary and commonplace dis- 

 tinctions between animals and 

 plants are in their opinion, both 

 obvious and sound. Is there any 

 liklihood, it may be asked, of our 

 confusing a bird with the tree on 

 whose kindly branch it perches? 

 Are we likely to mistake the ox 

 for the grass it crops? Or is there 

 any relationship whatever, between 

 the flower and the fair being whose 

 person it may serve to adorn, and 

 whose beauty it may enhance? 

 True, the bird and tree, ox and 

 grass, flower and wearer, are liv- 

 ing beings. All possess life; and 

 with this admission the likeness 

 and relationship may be thought 

 to end. There is no task, indeed, 

 for the performance of which the 

 popular mind may regard itself as 

 being better fitted, than that of 

 separating animals from plants. 

 And any suggestion to the con- 

 trary, and which would hint that 

 possibly we might experience some 

 difficulty in framing an exact defin- 

 ition of one group or the other, 

 would be naturally met with in- 

 credulity, and even scorn. Ani- 

 mals move, whilst plants are fixed; 

 animals possess no leaves or flow- 

 ers, whilst plants have both; ani- 

 mals have nerves and feel, plants 

 exhibit no sensations. The form, 

 the possession or absence of pow- 

 ers of motion, and the common at- 

 tributes of the life of each group 

 of living beings, thus serve, ap- 

 parently, and in the most satisfact- 

 ory manner, to map out with bold 

 outlines the limits of the plant 

 creation, as distinguished from 

 those of the animal world. 



Such is the philosophy of every- 

 day life. Scientific philosophy, 

 however, is forced to take a wider 

 view of matters than can be ob- 

 tained from the popular stand- 

 point; and one result of a more 

 comprehensive glance at the fields 

 of living nature is to throw very 

 considerable doubt on the validity 

 and worth of the common modes 

 of separating animals and plants. 

 The popular ideas deal with the 

 higher forms of animals and 

 plants, and concern themselves 

 with the separation of what may 

 be seen with the unassisted sight; 

 and with characters in animals and 

 plants that can be discerned with- 

 out any exercise of skill. But be- 

 yond the visible world lies a uni- 



verse of life, invisible save to the 

 eye of the microscopist. Other 

 worlds than ours rise at his beck 

 and call — worlds peopled with be- 

 ings so diminutive that their di- 

 mensions are estimated by stand- 

 ards compared with which a hair's- 

 breadth is to be esteemed gigantic. 

 In these regions of the infinite^ 

 small there are included beings 

 the exact nature of which, we shall 

 presently see, it may be hard or 

 impossible to discover. But even 

 within the visible portion of living 

 nature which exists around us, 

 there may be much on which the 

 far-seeing glance of science rests 

 that is dubious and uncertain. It 

 may be shown that in many cases 

 the common distinctions between 

 animals and plants are utterly 

 valueless when applied to the 

 classification of some tolarbly well- 

 known forms of life. The whole 

 question before us is one which 

 has grown out of the increasing re- 

 search of modern times; the ad- 

 vances of modern science thus re- 

 sulting in the demonstration of 

 our ignorance of many of the fields 

 of inquiry which lie before our 

 gaze. And in what follows we 

 shall endeavour to show, not mere- 

 ly that the task of separating some 

 animals from some plants is at- 

 tended with great difficulty, but 

 also that it may be impossible to 

 declare, in the present state of our 

 knowledge, what are the essential 

 characters of the animal, and what 

 the unmistakable features of the 

 plant. 



A simple experiment in the pro- 

 duction and development of some 

 lower forms of life, will serve as a 

 starting point for our inquiries into 

 the special characteristics of the 

 two great groups of living beings. 

 Some chopped hay is put in a 

 vessel, and through the addition 

 of some water an infusion thereof 

 is made. This infusion is further 

 allowed to stand freely exposed to 

 the air for a week or so, and at 

 the expiry of that period we place 

 a drop of the liquid under a micro- 

 scope of high power. Then a 

 wonderful sight bursts upon our 

 view. The fluid which the ordin- 

 ary observer might have expected 

 to be turbid from the presence of 

 particles derived from the dead 

 hay, is seen literally to swarm with 

 life. Rushing hither and thither 

 across the field of the microscope 

 are numberless specks, which our 

 first glance assures us are living 

 beings. When the eye has had 

 time to become better acquainted 

 with the scene on which it rests, 

 it may assort or parcel out the or- 



ganisms of the infusion into va- 

 rious kinds or grades. There, for 

 instance, are minute rod-shaped 

 bodies which wriggle aboutwithan 

 ill-defined, jerking motion. These 

 are bacteria. There, again, are 

 bodies of different form and larger 

 size, which appear to consist of a 

 number of the rod-like bacteria 

 united, end to end, and which the 

 biologist names vibrios. But we 

 also discern bodies which are dif- 

 ferent from either of the organisms 

 just mentioned, and which attract 

 attention from the rapidity of their 

 movements as they flit hither and 

 thither like swift vessels through 

 their miniature sea. Stay; there 

 is one of these active bodies which 

 has come to rest for awhile, and 

 which permits us, luckily, to ob- 

 tain a better view of its form and 

 nature. You notice it to be pear- 

 shaped, and if you are capable of 

 forming an idea of the size of the 

 minute objects with which the mi- 

 croscopist deals, you will not be 

 surprised to learn that the body 

 you see before you measures about 

 the three thousandth part of an 

 inch in length. This pear-shaped 

 speck bears at its narrow end a long 

 tail, formed of a filament which we 

 may compare to a miniature.eyelash, 

 and which has been named a cil- 

 ium. By more careful observation 

 we might see that a second ball, 

 or cilium, was present, and that 

 this latter appendage was also at- 

 tached to the slender extremity of 

 the body. The body itself pre- 

 sents few or no features for re- 

 mark. But if we are fortunate in 

 our selection and manipulation of 

 our specimen, we shall be able to 

 see within the body a clear round 

 space, which ever and anon con- 

 tracts itself with a jerk and disap- 

 pears, only, however, to reappear 

 with its clear surface as before. 

 Now the creature is off again on 

 its pergrinations, to add one more 

 unit to the hustling and jostling 

 crowds which people the drop of 

 water before us. You are able, as 

 it moves, to see that the longer of 

 the two tails, or cilia;; serves as a 

 kind of propeller, whilst the second 

 tail exists behind; and you may 

 sometimes observe the creature to 

 anchor itself by the second cilium, 

 and then spin round and round 

 the fixed point like some curious 

 top of vital construction. Then it 

 releases itself, and is off again on 

 its wild career — jostling its friends 

 and neighbors in the struggle for 

 existence in which animalcule and 

 man appear alike to participate. 

 (TO EE CONTINUED. ) 



