CH. VII} 



SERIAL SECTIONS 



193 



(1) Put the right side of the embryo next the microtome holder, then the 

 left side will be cut first. 



(2) Let the caudal end meet the knife edge. 



(3) Put the first section in the upper left hand part of the slide as in the 

 other cases. The sections will be lengthwise of the slide. This will bring the 

 ventral side up and the head to the right on the slide. Under the microscope the 

 head will appear at the left and the dorsal side toward the upper edge of the slide. 



\ 304. For serial sections with collodion imbedded objects it is a great advan- 

 tage to have the imbedding mass unsymmetrically trimmed, so that if a section is 

 accidentally turned over it may be easily noticed and rectified. 



Furthermore it is imperatively necessary that the object be so imbedded that 

 the cardinal aspects, dextral and sinistral, dorsal and ventral, cephalic and caudal, 

 shall be known with certainty. 



\ 305. Thickness of Cover-Glass and of Serial Sections. — It is a great advan- 

 tage to use very thin cover-glasses ( 0.12-0. iS mm.) for serial sections, then the 

 cover will not prevent the use of high powers. When the ordinary slides (25 X 

 76 mm., \/ 3 inch) are used cover-glasses 24 50 mm. may be advantageously 

 employed. 



79 

 5 

 10 



86 



T- 



93 









 



HOI! 



\0 

 







Homo 5 

 Slide 10 

 See' a 79 



20m 100 

 1901 







Fig. 162. 







Fig. 162. A slide of serial sections showing the position of the sections, the 

 label and the size of the cover-glass {24 x 50 mm. ). The numbers next the cover 

 at the left indicate the first section of each row, and illustrate the method of placing 

 the sections as if they were words on a printed page. T. Transections. 



The combined thickness of the sections on a slide is easily determined by not- 

 ing carefully the position of the microtome screw at the first and last sections and 

 measuring the elevation. With good modern automatic microtomes the successive 

 sections are almost exactly uniform in thickness, hence it is easy to determine the 

 combined thickness of the sections on a slide. 



\ 306. Labeling Serial Sections. — The label of a slide on which serial sections 

 are mounted should contain at least the following : 



The name of the embryo and the number of the series ; the number of the 

 slide of that series ; the thickness of the sections, and the number of the first and 

 last section on the slide ; the date. It is also a convenience to have the informa- 

 tion repeated in part on the left end and the number of the first section in each 

 row, as shown in the sample slide of serial sections. (Fig. 162). 



