114 



ANIMALCULE. 



As those creatures appear in every liquid and in- 

 fusion which is adapted for them, if freely exposed to 

 the air, the origin of the germs has been a matter of 

 curious inquiry ; but if we compare the size of the 

 eggs in the roe of a fish, when they are shed, and con- 

 sequently matured, with the size of the fish when 

 full grown, and apply the analogy, with every allow- 

 ance, to the animalcules, we shall find that, until 

 some microscope of much greater power shall be 

 invented, it will be in vain to attempt to find their 

 minute rudiments. In a fish which attains the 

 weight of 25 pounds, the egg does not weigh more 

 than l-100th part of a grain, or, in round numbers 

 the fish may be 175,000 times the weight of the egg 

 in the roe. The cube root of that, in the propor- 

 tional dimensions in line is, making allowance for the 

 more regular shape of the germ, about l-60th of that 

 animal. Now many of the common animalcules re- 

 quire a magnifying power of 500, and some of them of 

 800 in line, before they are distinctly visible ; and, sup- 

 posing the germ to be in proportion as above stated, it 

 could not be seen without a power in line of 30,000, 

 which, according to the usual estimate, would require 

 a focal length of only 1 -300th of an inch, an instru- 

 ment which could not be constructed upon any prin- 

 ciple at present known in the arts. It may be pro- 

 per to mention that the magnifying power, in surface, 

 is 900,000,000 ! or one which, if it could be applied, 

 would make the floor of Westminster Hall appear as 

 large as all England. 



But minute as those germs must be, and vain as is 

 the hope of finding them in their rudimental state, 

 they are as much within the action of the common 

 laws of nature as those of the largest animals. The 

 action of the air is necessary for their development. 

 The experiment of Spallanzani is conclusive upon 

 this point, though it does not warrant the conclusion 

 which he draws that the germs necessarily descend 

 from the air. They are indeed so very minute that 

 it is impossible to imagine an atmosphere so still as 

 not to move them about, and difficult to imagine a 

 place where they cannot find entrance. Spallanzani's 

 experimental vessels contained infusions which had 

 been boiled for an hour. Some of them were left 

 open, others closed with cotton wool, a third set had 

 wooden stoppers, and the fourth were hermetically 

 sealed. At the end of twenty-five days there were 

 animalcules in them all ; very abundant in the open 

 ones, and less and less so in the others, till in the 

 sealed vessels they were very few. A film of oil on 

 the surface of the infusion had nearly the same effect, 

 and apparently from the same cause, that of prevent- 

 ing the action of the air. 



It is by no means impossible that the germs of 

 animalcules may ascend with water in the process of 

 evaporation, and descend again with the rain ; and it 

 may be also that they are carried by the water into 

 the earth, and flow out again into the most pure and 

 limpid springs ; but the developed animals are very 

 rare in water in its pure state, so that, as is the case 

 with the spawn of fishes, the eggs of insects, and the 

 seeds of plants (with all known germs of living crea- 

 tures indeed), a specific elementary action is neces- 

 sary for their development. 



That action appears to be heat and humidity 

 jointly, and the heat appears to be in part derived 

 from the putrid fermentation ; as they are not only 

 brought forward by artificial infusions, but appear in 

 all shallow waters where vegetable matter is in a state 



of decomposition ; and as they are found in vinegar 

 and in sea-water, they can at feast endure the acid 

 and salt which are in these. That they can exist in 

 pure vinegar, or vinegar in which there is no vege- 

 table mucilage, is not probable ; and they are pre- 

 vented from being developed by a small admixture of 

 sulphuric acid with common vinegar, which hinders 

 the formation of " mildew " as it is called by dealers. 

 From the observations and experiments of Dr. Power, 

 it appears that these inhabitants of vinegar (vibrio 

 aceti) have some peculiarities of character. If the 

 temperature is raised a little above that of the human 

 body in a state of health, they die ; but they can 

 bear to be frozen in the vinegar and again thawed out 

 of it. They do not, however, bear this intense cold 

 patiently or willingly, for they escape if they can, even 

 into a substance in which they are not naturally 

 produced. 



The structure and functions of animals so very 

 minute cannot, of course, be well understood ; but 

 still enough has been gleaned, partly from one 

 partly from another, for enabling at least a rational 

 guess to be formed. They all have a mouth and 

 stomach, of some form or other ; and some of them 

 are as ravenously carnivorous, and eat up their 

 brethren with as much avidity and gusto, as the most 

 voracious fishes. Some of them are pofygastric, or 

 have many stomachs, in the form of little sacs united 

 by tubular connexions ; and others are monogastric, 

 or one-stomached, and have generally alimentary 

 canals. Of course nothing is known of the nervous 

 or circulating systems of animals so minute ; and the 

 existence of these is inferred rather than proved. 

 Some are furnished with eyes ; and all have some 

 means of perception by which, to a certain extent at 

 least, they keep themselves out of danger. Muscles, 

 and other organs of a considerable degree of compli- 

 cation, have been distinctly observed in several of the 

 larger ones ; and as they are all locomotive, and 

 some have the power of attaching themselves to 

 other bodies by means of little hooks or otherwise, 

 and all of them can partially alter their shape, it is 

 probable that the whole have muscular systems more 

 or less complicated in proportion to their functions. 

 Some of these muscles must be exceedingly minute, 

 not the ten-thousandth part of an inch in length, or 

 the millionth in thickness ; and yet they are probably 

 made up of fasciculi containing as many fibres and 

 contracting on the very same principle as those of the 

 largest animals. It does not appear that any cf them 

 have internal bones ; but they seem all to be invested 

 with an integument sufficiently tough for allowing of 

 insertion of the muscles ; and some are covered with 

 shells which, in some of the species, are regular bi- 

 valves, and when the valves are shut enclose the 

 whole body. 



Some are coloured, but the greater part are nearly 

 colourless, and some are quite transparent, so that 

 they are seen by the refraction and reflection of light 

 at their surfaces ; and it affords a wonderful proof of 

 the delicacy and divisibility of light, when we con- 

 sider that it can be differently acted on by the several 

 parts of the bodies of creatures of which the whole 

 mass is so small. 



Their modes of reproduction are not the least 

 curious part of their economy ; and in these, as in 

 some other matters, the different species resemble 

 more than one class of the larger invertebrated 

 animals. Some propagate by spontaneous division ; 



