ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 965 



In England, this view has not been accepted in practice, and an 

 histologist who attempted to determine the true structure of an 

 object by experimental or theoretical optical considerations was a 

 rarissima avis indeed. 



A very curious illustration of the mistakes that must inevitably 

 result from this neglect will be found in a paper which has recently 

 appeared by Mr. J. B. Haycraft " Upon the Cause of the Striation of 

 Voluntary Muscular Tissue," * in which the author, with much care 

 and ingenuity, reproduces the twice reproduced view of Mr. Bowman, 

 that the striation of muscular tissue is simply an optical effect caused 

 by the undulating shape of the fibres. 



The paper evidently commended itself to histologists of eminence, 

 as it was printed at length in the ' Proceedings of the Eoyal Society,' 

 and reprinted in the ' Quarterly Journal of Microscopical Science,' and 

 so far microscopists may congratulate themselves upon the acceptance 

 in principle of a point on which they have hitherto vainly en- 

 deavoured to make themselves heard ; but the paper points a still 

 further moral in regard to the importance of a knowledge of the 

 theory of microscopical appearances, for the author (who describes 

 his paper as an attempt to explain the structure of muscle " on simple 

 laws of geometrical optics") was unaware that, as established by 

 Professor Abbe, there is a limit beyond which the laws of geometrical 

 optics have no application, and that it is useless to attempt to reason 

 as to the appearances presented by an object which requires a power 

 of 500 times from those presented by one which requires a power of 

 only 50 times. The laws of refraction in particular, for instance, no 

 longer holding good in the case of minute objects, and cylindrical 

 threads entirely losing the characters of refracting bodies which are 

 distinctly exhibited by similar objects of larger size. 



Whilst, therefore, the author is worthy of every commendation for 

 his adoption of a method hitherto too generally neglected, the basis 

 on which he rests his conclusions is unsound in consequence of the 

 error into which he fell at starting. 



We subjoin some extracts from Mr. Haycraft's paper which will, 

 we think, be of interest to microscopists : — 



" We can account for all these cross markings in a way which 

 involves no theory, and requires for its appreciation but a knowledge 

 of most elementary geometrical optics. If a small fragment of muscle 

 be teazed out in water, salt solution, or almost any other fluid, and 

 examined in the ordinary way, with a power of 300 diameters or 

 more, the important fact may be made out (which is the basis of all 

 my future observations) that the borders of the fibres are not smooth, 

 but undulate, presenting wavy margins. 



" In the fresh, unstained preparation there is a halo around the 

 edge of the fibre which masks the crenulated border, yet by carefully 

 adjusting the mirror so as to obtain oblique light, or by searching for 

 a fibre partly in the shade of another, this may always be made out ; 

 in the case of insects' muscle, this is, however, always easy to demon- 

 strate, for the fibres are much coarser, indeed, the appearance has 

 * Proc. Koy. Soc, xxxi. (1881) pp. 360-79 (1 pi.). 



