ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 127 



be made between the normal living contractions and the permanent con- 

 tractions which are accompanied by a partial destruction of the muscle- 

 fibre, and that the latter only are marked by an increase of refractive 

 power. 



So far we have given an abstract only of the author's paper. His 

 "Eemarks on our Knowledge of the Structure of the Transversally 

 Striated Muscle-fibres " which follow, we translate in extenso. 



"It seems to me therefore that the very contradictory data con- 

 cerning the anatomical relations of a muscle-fibre during contraction 

 require revision. It will be asked why I do not undertake this revision. 

 The answer is, that such a revision is not possible without an accurate 

 knowledge of the relaxed muscle-fibre, and that I feel myself unable to 

 form an opinion as to whether certain results of late investigations on 

 this subject are reliable or not. I regard not only myself but others 

 also provisionally as unable to form this opinion for reasons which will 

 be explained in the following remarks. 



Where twenty years ago a distinction was only drawn between 

 singly and doubly refracting substance in the muscle, there is now 

 recognized a sequence of the parallel layers (using Eollett's nomencla- 

 ture) Z, E, N, J, Q, h, J, N, E ; nine layers in place of two ; these 

 layers are conveniently described as of a thinness which approaches ' the 

 limits of the perceptible.' 



If we consider that the whole of geometrical optics, i. e. the recognized 

 laws of the formation of images, only holds good so long as the relation 

 between the magnitude of the object and the wave-length of light does 

 not fall below a certain limit ; * and if we consider, further, that the 

 wave-length of light in air (e. g. for the line C t) is • 000589 mm., 

 and in muscle-fibre (n = 1-3G3) is 0*000432 mm., and that these 

 numbers are greater than the thickness of the single layers, we must 

 ask ourselves whether these anatomical results have any value at all. 



To this it must be added that Abbe, the first living authority on 

 the theory of the Microscope, says with regard to the diffraction-images 

 produced by the transverse striation of the muscle-fibres, ' The 

 manifold changes in the character of the image ' (produced by the trans- 

 verse striation) ' explain to some extent the well-known difference between 

 the observations of various investigators with regard to these appear- 

 ances, but prove also the impossibility of acquiiing ( any definite knowledge 

 about their actual physical structure ' (i. e. of the fibres) ' in the sense of 

 the attempts which have hitherto been made.' f 



Thanks to the investigations of the same physicist, we now know 

 that the formation of a true microscopic image depends upon whether all 

 those rays contribute to the formation of the image on the retina which 

 are diffracted by the boundaries (whether sharply defined or gradual) 

 between parts of the object of different refractive powers, or by inequali- 

 ties of the object, &c. If this is not the case we may receive illusory 

 images ; the finer the structure which we attempt to resolve by the 

 Microscope, the greater is the probability that a portion of the diffracted 

 rays will not reach the eye. Beyond a certain limit of fineness this 

 probability becomes a certainty, and Abbe concludes ' that no Microscope 

 has ever shown, or ,will ever show, anything actually existing in the 



* Of. Helniholtz, " Ueber die Grenzen cler Leistungsfahigkcit des Mikrokopes," 

 SB. Berliner Akad., 1873, p. 625. 



t According to Ditscheiner. J Arch. f. Mikr. Anat, ix. (1873) p. 454. 



