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generated by the action of certain currents of air, or 

 the eggs from which the various blights or grubs 

 are produced must be floating about in the air, or, 

 lastly, the prevalence of certain winds must have 

 an influence in giving birth to animals enclosed 

 in eggs deposited by parent insects upon the spot 

 upon which the blight is seen. As the first of these 

 propositions depends entirely upon the doctrine of 

 equivocal generation, a doctrine which is exploded by 

 every naturalist (except such as endeavour to supply 

 from their own prejudiced imaginations those points 

 in the economy of nature which the minuteness of the 

 objects or the difficulty of their investigation have ren- 

 dered it next to impossible to prove by actual exami- 

 nation), we shall enter into no attempts to refute it, 

 merely observing that in every instance amongst 

 insects where an attentive observation has been made 

 upon the nature of their production, it has been found 

 that the birth of every individual has been the result 

 of the impregnation of the female and the subsequent 

 development of eggs, which are either hatched after 

 deposition, or within the body of the parent. The 

 second proposition, however, that the eggs are carried 

 about in the air, merits more particular observation, as 

 it depends upon a theory adopted by many distin- 

 guished writers. Thus, Dr. Good observes, " That 

 the atmosphere is freighted with myriads of insect 

 eggs that elude our senses, and that such eggs, when 

 they meet with a proper bed, are hatched into a per- 

 fect form, is clear to any one who has attended to the 

 rapid and wonderful effects of what in common lan- 

 guage is called a blight upon plantations and gardens," 

 and in like manner the eloquent Chalmers, dis- 

 coursing upon the boundlessness of the creation, ob- 

 serves, " About the time of the invention of the tele- 

 scope another instrument was formed, which laid open 

 a scene no less wonderful, and rewarded the inquisitive 

 spirit of man. This was the microscope. The one led 

 me to see a system in every star, the other leads me 

 to see a world in every atom ; the one taught me that 

 this mighty globe, with the whole burden of its people 

 and its countries, is but a grain of sand on the high 

 field of immensity, the other teaches me that every 

 grain of sand may harbour within it the tribes and the 

 families of a busy population. The one told me of 

 the insignificance of the world I tread upon, the other 

 redeems it from all its insignificance, for it tells me 

 that in the leaves of every forest, and in the flowers of 

 every garden, and in the waters of every rivulet, there 

 are worlds teeming with life, and numberless as are 

 the glories of the firmament. The one has suggested 

 to me that beyond and above all that is visible to 

 man, there may be fields of creation which sweep 

 immensity along and carry the impress of the 

 Almighty's hand to the remotest scenes of the 

 universe, the other suggests to me that within and 

 beneath all that minuteness which the aided eye of 

 man has been able to explore, there may be a region 

 of invisibles, and that could we draw aside the myste- 

 rious curtain which shrouds it from our senses, we 

 might see a theatre of as many wonders as astronomy 

 has unfolded a universe within the compass of a 

 point so small, as to elude all the powers of the 

 microscope, but where the wonder-working God 

 finds room for the exercise of all his attributes, where 

 he can raise another mechanism of worlds, and fill 

 and animate them all with the evidence of his glory. " 

 This is a beautiful view of the subject, and far be it 

 from us to lessen its effects, by limiting any of those 



fine ideas to which it will naturally give rise. Still 

 we are compelled, to a certain extent, to narrow its 

 acceptation. That the microscope discovers an in- 

 finity of animalcules, far too small for our unaided 

 sight, is not to be doubted ; and that numberless 

 others, which the microscope cannot reach, exist, is 

 perhaps equally certain ; but it is in fluid matters that 

 the most minute of these creatures are found. If they 

 floated in the air, or if they pervaded all substances, 

 it cannot be doubted that the field of a high-powered 

 microscope would necessarily discover some of the 

 larger of them wafted about within its focus, when 

 " nothing but emptiness" was placed within its power. 

 But this is not the case ; an observer may watch all 

 day, and he will not see any aerial monster, invisible 

 to human unassisted sight, pass across his field of 

 view ; but let him place the smallest drop of fluid in 

 the focus of his microscope, and it will be found to 

 swarm with life, so as fully to warrant all the eloquence 

 which Dr. Chalmers has used upon the subject. In 

 this point of view, therefore, the question assumes a 

 high degree of importance, as connected with a cir- 

 cumstance which has been repeatedly noticed irf 

 various works relative to that dreadful scourge which 

 unfortunately appears to have taken up its abode 

 with us we allude to the cholera morbus. By some 

 writers this pestilence has been considered as attri- 

 butable to swarms of insects. Thus it is recorded, as 

 a curious fact, that its arrival at Moscow was preceded 

 by a cloud of little green flies, which darkened the 

 air, and covered persons from head to foot when they 

 entered the streets, which flies, by some medical men 

 (see Neale on Animate Contagion), have been thought 

 to have a considerable influence in propagating the 

 disease. On the other hand, it was stated in the 

 public journals, that in some places flies had entirely 

 disappeared on the breaking out of this plague ; and 

 yet, within a very few weeks, it has been mentioned 

 in the American papers, that the flies which, at the 

 period of the former breaking out of the disease, had 

 disappeared, were now swarming. Now, all these 

 seem to have been circumstances of not very extra- 

 ordinary occurrence, which have, nevertheless, been 

 seized upon by persons whose attention has been 

 more especially directed to the phenomena of natural 

 objects for the purpose of discovering the nature of 

 the disease in question. Thus the flight of myriads 

 of green flies was evidently a swarm of aphides, 

 similar instances of which, unattended by the disease 

 in question, or any other malady, are recorded in 

 works upon Entomology. That such view of the 

 subject is not far from correct, may be presumed from 

 the fact, that the appearance of the disease has not, 

 except in the few recorded cases, been attended by 

 those flights of insects ; whereas, had they been the 

 real causes of the cholera, they would necessarily have 

 been noticed wherever this dreadful malady had shown 

 itself. Other medical men, however, entertained an 

 opinion, which seems to be perfectly analogoul to the 

 supposed cause of blight. Thus Dr. Hahnemann 

 considered that the disease was caused by insects, 

 but which are invisible to the naked eye, and which 

 adhere to the skin, hair, and clothes a perfect blight, 

 in fact, according to the most approved acceptation 

 of the word. Let us, however, look a little further 

 into the nature of the blight of our fruit-trees, and we 

 shall perhaps be enabled, by analogy at least, to 

 demonstrate, that the fearful disease in question does 

 not originate in the manner above noticed. 

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