Ch. XI] SERIAL MICROSCOPIC SKCTIONS 399 



serial order. Do not use water for spreading the sections, but one 

 of the iodin stains for glycogen (§ 575). The glycogen will be stained 

 at the same time that the sections are spread. 



Let the sections dry thoroughly after spreading. Deparaffin with 

 xylene and mount in yellow vaseline or use thin xylene balsam, but 

 do not put a cover-glass over the balsam preparations. 



The iodin stain remains in the spread sections for ten years or longer. 

 One can restain any time by putting the slide with the spread, but 

 not deparafhned sections, in a shellvial of the iodin stain. It is pos- 

 sible also to stain the nuclei with hematoxylin in the same way. If 

 this is done the hematoxylin should be used first and washed off with 

 water and the iodin stain be used last, but not washed off with water. 



Advantages of Histological Serial Sections 



§ 649. General on series. — It is coming to be appreciated more 

 and more that in histology as well as in embryology one can only get 

 a complete knowledge of structure by having the entire organ cut in 

 microscopic sections and each section mounted in order. Further- 

 more, it is necessary to have the organ cut in three different planes. 

 In this way one can see every aspect of the structural elements and 

 their arrangement in the organs. 



In single sections one gets only a partial view. For example, how 

 many students have any other idea of a ciliated cell than that it is 

 a cell with triangular outline with a brush of cilia at the board end. 

 Probably many would be puzzled if they had a top view of the ciliated 

 end; and the attached end would be even more puzzling. 



It may not be possible for every worker to make serial sections 

 of all the organs in all the three planes, but every one who is working 

 seriously in histology can make all his preparations serial ; that is, the 

 sections which are mounted can be in serial order; then a puzzling 

 appearance in one section may be perfectly intelligible in one a little 

 farther along. 



To get the greatest benefit from serial as indeed also from single 

 sections, the sections should be made in a definite manner; that is, 

 they should be exactly across the long axis of an organ or parallel 

 with the long axis {Transections and Longisections). 



