MICROSCOPE. 



357 



minute, which is not capable of being resolved 

 into smaller particles, as far as our means of 

 observation can carry us; and the absurdity of 

 the particular dimensions assumed is further 

 shown by the fact, now well known, that there 

 are very numerous species, and countless indi- 

 viduals, among the Polygastric animalcules, 

 whose whole bulk is much less than that of one 

 of the so-called ultimate particles, and which 

 contain within this a considerable number of 

 different organs. The following statements 

 made some years since by Ehrenberg will give 

 a very good idea of the mode in which the 

 size of such organs and of their component 

 parts may be approximately known, when they 

 are themselves too minute for measurement. 



" I could plainly distinguish with a micro- 

 scope magnifying nearly 800 diameters, Mo- 

 nads, which were filled with colouring nutritive 

 substances, and which possessed voluntary mo- 

 tions, but the entire and greatest diameter of 

 whose body only amounted to the n^th or 

 jg^th of a Parisian line. I could perceive 

 in the largest individuals of this form as many 

 as six, and in the smallest as many as four, in- 

 ternal sacs coloured blue by indigo, which at 

 times did not occupy half the internal dimen- 

 sion of the animal. Such a sac, therefore, of 

 an animalcule measuring T ^th of a line, 

 and if we suppose only four sacs occupying the 

 half of it, (therefore not one of the smallest,) 

 is ijrojjth of a line in size. Further, if we 

 suppose the single colouring particles, with 

 which the stomachs are filled, not to be nume- 

 rous, it would be against all probability not to 

 think that they were filled by several particles. 

 Let us, however, only suppose each sac to 

 be filled with three colouring atoms, which, 

 from the roundness made perceptible by the 

 motion communicated to them when diffused 

 through the water, we may well admit, this 

 alone affords a proof of the existence of material 

 colouring particles of red and dark blue moving 

 freely in water, which measure ^'^th of a 

 line, or ^^th part of an inch in diameter; 

 and calculating these objects from the smallest 

 of the animalcules, which by actual observation 

 were found to be 5D kgth of a line in size, and 

 which sometimes contained four coloured points 

 in the hinder part of the body, these particles, 

 which cannot be distinguished individually by 

 the eye with a magnifying power of 800, but 

 which are yet to be recognized as corporeal, 

 would amount to j^to of a line, or 

 srojjjo 1 ' 1 of an inch. Further, the smaller 

 monad-stomachs are seen isolated in the body, 

 and with sharp outlines. In larger Infusoria, 

 which are -^th of a line, or more, in diameter, 

 these internal receptacles are recognized as evi- 

 dent membranaceous sacs, which often make 

 their appearance isolated, when the animalcule 

 is pressed, or when it divides itself, and which 

 have been supposed to be separate infusoria, 

 internal monads. It can be distinctly seen 

 that, when two such digestive sacs touch one 

 another, the thickness of the partition between 

 them is, in comparison with the diameter of the 

 stomach, extremely small, so that the former is 

 scarcely perceptible ; it may be reckoned as at 



the most JLth of the latter, Granting, how- 

 ever, the thickness of the partition to be as much 

 as fgtli the diameter of the sac, this would 

 amount to ygJ^th of a line, or 73^5 th 

 of an inch, in monads s^th of a line in 

 size, in which the stomachs measure but one- 

 eighth of the whole length of the body, and 

 are therefore igg^th of a line in diameter." 

 When similar views are extended to the young 

 of the species on which this calculation is 

 founded, or to smaller species in the existence 

 of which there is good reason to believe, the 

 minuteness of structure thus disclosed becomes 

 still more wonderful. " Let not these calcu- 

 lations," it is justly remarked by Ehrenberg, 

 " be regarded as playful ; they are so far in 

 earnest, that they are founded on the contem- 

 plation of nature, and are not to be considered 

 as a groundless speculation. They plainly de- 

 monstrate an unfathomableness of organic life 

 in the direction of the smallest conceivable 

 space; and if the word infinity be too much for 

 what we know at present, let the word unfa- 

 thomableness, which I have purposely em- 

 ployed, avert from me the reproach of exagge- 

 ration, and establish the direction which the 

 physical, chemical, and physiological enquiries 

 of our days, should they be rendered fruitful by 

 new powers, have to take, and what deviations 

 they have to avoid." 



To these enquiries Ehrenberg has subjoined 

 an attempt to calculate the power of vision for 

 the human eye, and the ultimate power of the 

 microscope. From his experiments on the 

 smallest square magnitudes which are ordina- 

 rily visible at any distance by the human eye, 

 he finds that they vary in different cases from 

 g'gth to -j^th of a line ; but when strongly il- 

 luminated, much smaller bodies can be seen, 

 metallic particles of ^th of an inch being 

 visible in common daylight ; and non-transpa- 

 rent threads of -j^th of a line in thickness 

 being distinguished, when held between the 

 eye and the light. Hence the size of the mi- 

 nutest objects visible with a given magnifying 

 power of the microscope might be determined 

 by dividing their apparent dimensions, as just 

 stated, by the magnifying power; thus no 

 square corpuscles of less dimension than 

 3 S ' 55 th or 4S ^jth of a line could be seen with 

 a magnifying power of 100 diameters. In 

 practice, however, owing to the degree of im- 

 perfection which must necessarily attend the 

 best-constructed instruments, the minuteness of 

 the smallest visible objects cannot be judged of 

 entirely by this rule ; since, in order that it 

 should be correct, it is necessary that the 

 object of jg^jjth or ^th of a line in dia- 

 meter, should be represented to the eye as 

 clearly by a microscope magnifying 100 dia- 

 meters, as a real object of ? ' 5 th or ^th of a 

 line would be; this is very far from being the 

 case, owing to the loss of light by reflection in 

 passing through the lenses, as well as to the 

 errors of the lenses themselves, which can never 

 be perfectly corrected. With a magnifying 

 power of 1000, which is perhaps the highest 

 that has yet been employed to real advantage, 

 the minutest particle which could possibly be 



