280 PROGRESS OF MICROSCOPICAL SCIENCE. 



a magnifying power of from 200 to 500 diameters, or that obtained 

 by a Hartnack's objective 8 and eye-piece E or F. .The structure of 

 normal uncontracted transversely striated muscular fibre is: (1) A 

 light very slightly refracting band divided into two halves by (2) a 

 dark highly refractile stria ; (3) a moderately dark, tolerably strongly 

 refracting band, in the middle of which is (4) a brighter, less refract- 

 ing stria. In every fibre with very broad transverse stria? the simple 

 dark band can be resolved with high powers into three : a middle 

 darker one, and two lateral clearer or brighter ones. Hence we must 

 admit that such division still exists even where our present means of 

 research do not permit it to be seen. Throughout his paper Engel- 

 mann makes use of the following terms : the stria in the middle of the 

 isotropal substance he calls the intermediate disk (zwiscliensclieibe) and 

 the adjoining stria? secondary or accessory disks (nebenscheiben). Both 

 of these together, when they cannot be distinguished as separate, 

 constitute the fundamental membrane (Grundmembran of Erause); the 

 middle layer of the doubly refracting substances forms the median 

 disk of Hensen, and the two lateral he terms transverse disks. In the 

 closely striated muscles of vertebrata z and n appear united together 

 to form a single and simple foundation membrane in which no sub- 

 division can be seen. The distinctly striated fibres of insects, on the 

 other hand, show the division well, and the whole series of disks in 

 one compartment are here sometimes as much as four times thicker 

 than in vertebrata. The height of each set varies even in different 

 muscles of the same animal. The greatest height or length of one 

 compartment Engelmann found to occur in the abdominal muscles of 

 insects where it amounted to 0*011 mm. The isotropal and aniso- 

 tropal substances are about equal in height, the proportion of the 

 former to the latter being as 6 : 7. The degree of transparency of the 

 several parts varies considerably, so that now one, now another, may 

 be the darker. Where both are of equal transparency the existence of 

 transverse stria? may at first sight be almost overlooked. The distinc- 

 tion is always well brought out by the polariscope. The remainder 

 of the paper is occupied with a special description of each disk in 

 succession. From his examination of muscle under polarized light 

 and by other means he has arrived at the conclusion that muscular 

 tissue is composed of an infinite number of rods arranged parallel to 

 the longitudinal axis of the fibres which are naturally in immediate 

 contact with each other, but which after death, or after treatment with 

 reagents, shrink and exude or excrete the isotropal substance. The 

 size and form of the rods he supposes to differ in each of the disks 

 that make their appearance in the above scheme. See also 'The 

 Academy,' May 1st, which contains an illustration explaining the com- 

 plexity of the structure. 



A Protozoon in Urine ! — V. C. E. Nelson says, in the ' New York 

 Medical Journal ' (March), that a gentleman recently brought him a 

 phial of his urine to examine under the microscope : nothing what- 

 ever was seen, with the exception of a single protozoon, which forms 

 the subject of this communication. Two phials were brought on that 

 day ; in the urine of one only was this protozoon seen ; the urine was 

 not left in any open dish, but in a well-corked phial, so that the pro- 



