1G4 SUMMARY OF CURRENT RESEARCHES RELATING TO 



(fig. 38), each of which is slightly conical (fig. 39), so that tho one 



tits into its neighbour very easily. The upper side has a hovelled edge 



c, which prevents too extended a contact of the 



Fig. 38. membrane with the inner ring when the membrane 



is stretched. The rings are made of vulcanite, a 



substance which is not attacked by the ordinary 



reagents, such as spirit, Midler's fluid, acids, &c. 



When stretched on these rings, the object M — 



mesentery, epiplasm, &c. — may be placed beneath 



the Microscope and subjected to stains or fixative 



Fig. 39. or other reagents, such as nitrate of silver. 



Determination of the Number of Trichinae or 

 other Animal Parasites in Meat.* — This is thus 

 effected by Prof. H. Gage : — After meat has been 

 found to be infested with parasites, if it is desired 

 to determine the number in a kilogram, pound, or any other weight, a 

 section of the meat is made with some sharp instrument, and the thick- 

 ness of the section is measured by placing it between two cover-glasses 

 whose thickness is known, and then, after pressing the cover-glasses quite 

 firmly together, measuring the entire thickness. The thickness of the 

 section of meat is then easily determined by subtracting the thickness 

 of the cover-glasses from the number representing the thickness of the 

 cover-glasses and the meat. The sections may be from 0" 1 to 0*3 mm. 

 in thickness. Eemove the upper or eye-lens of the ocular of the 

 Microscope, and place on the diaphragm a piece of paper in which a 

 small square opening has been made, thus converting the diaphragmatic 

 opening from a round to a square one. Replace the lens, and by the aid 

 of a stage micrometer determine the value of one side of the square field 

 thus made. The opening need not, of course, be square, but it is much 

 easier for most persons to determine the area of a square than a circle — 

 hence a square is recommended. Put the section of meat under the 

 Microscope and count the number of parasites in the field, moving the 

 specimen and making twenty or more counts, in order to get an average 

 which shall fairly represent the number of parasites in one field. Find 

 the cubic contents of one field by multiplying the thickness of the 

 section by the number representing the value of the sides of the square 

 field. From this compute the number of parasites in an entire cubic 

 centimetre. Divide this number by the specific gravity of muscle 

 (1*058), and the result will give the number of parasites in one gram 

 of the meat. From this the number in one kilogram may be obtained 

 by simply adding three cyphers (multiplying by 1000), or in one pound 

 avoirdupois by multiplying by 453,593, which is the number of grains 

 in one pound. The following is an example : — 



The thickness of the section was ■ 27 mm., and the value of the 

 square field as seen in the ocular was 1 ■ 5 mm. The average number of 

 Trichinae seen in this field in twenty observations of different portions of 

 the meat was three. The cubic contents of the field was 0-27 x 2-5 

 X 1*5 = 0*6075 cub. mm. If 0*6075 cub. mm. contains three Tricliinse, 

 one cub. mm. will contain 4*038 of them, and a cubic centimetre or 

 gram would contain 1000 times as much, or 4938 Tricliinse, providing it 

 weighed only as much as distilled water at 60° F. But as muscle weighs 



* St. Louis Med. and Surg. Journal, liii. (1887) pp. 289-91. 



