THE CELL-THEORY 247 



of science — and at the end of the eighteenth century it required all 

 the genius of Bichat to sift the wheat from the chaff, amongst, the 

 great mass of facts which the observation of the past ages had 

 accumulated — and strengthening whatever place was weakest by new 

 investigations — to establish these very two propositions, upon a broad 

 and henceforward firm foundation. Great as was the service which 

 Bichat rendered in this way to biology — and wide as the difference 

 between the treatise ' De Partibus Similaribus ' and the ' Anatomie 

 Generale ' may be — still the one is the intellectual progeny of the other, 

 and exhibits neither alteration nor improvement in the method pursued. 



In the meanwhile, however, an aid to investigation had arisen, by 

 the means of which this method could be pushed to its uttermost 

 limits — we refer to the invention of the microscope. The influence of 

 this mighty instrument of research upon biology, can only be compared 

 to that of the galvanic battery, in the hands of Davy, upon chemistry. 

 It has enabled proximate analysis to become ultimate. Without the 

 microscope the ultimate histological elements were, as we have seen, 

 defined negatively , as parts in which any further structural difference 

 was too small to be detected. The microscope, on the other hand, 

 enables us to define the tissues positively — to say, a given tissue has 

 such a structure, and magnify it as you will, it will present no further 

 differences. 



The amount of such positive information as to the ultimate 

 structure of the tissues, collected by Leuwenhoek, Malpighi, and 

 their successors, between the middle of the seventeenth and the 

 fourth decade of the present century, was very great, and in fact 

 the most important and characteristic features presented by the 

 histological element of plants and animals may be said to have been 

 well made out, at the time of the appearance of the celebrated treatises 

 by Schleiden and Schwann, cited at the head of this article ; and 

 these writers, therefore, added but little to the body of knowledge in 

 this direction. It is most unquestionable, however, that the biological 

 sciences, and more especially histology, received a wonderful stimulus 

 at their hands. Whatever cavillers may say, it is certain that histology 

 before 1838 and histology since then, are two different sciences — in 

 scope, in purpose, and in dignity — and the eminent men to whom we 

 allude, may safely answer all detraction by a proud " circumspice!' 



But wherein does the real value of their work lie ? We think this 

 question may be readily enough answered by those who admit the 

 force of what has been said in our opening paragraphs — who acknow- 

 ledge that mere anatomy does not exhaust the structure of living 

 beings — and that before histology can be said to be complete, we must 



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