4 02 SERIAL MICROSCOPIC SECTIONS [Ch. XI 



tions should be passed from the deparamning xylene to the iodized 

 alcohol (§ 576). After half an hour or more the slides are passed 

 through pure 95% alcohol, and back to the xylene or to carbol- 

 xylene. Then they can be mounted in balsam. 



§ 655. Staining for series. — There is a great advantage in point 

 of time and safety in staining the entire embryo in some good stain 

 like borax carmine (§ 548). Carmine is a very permanent stain also. 

 For bringing out special structural details the sections are stained 

 on the slide as described in § 639-640. The slide baskets are almost 

 a necessity for serial work (fig. 231-232), as the slides are handled 

 individually only twice, (1) when they are spread and dried and put 

 into the baskets, and (2) after all the processes are complete and the 

 sections are to be mounted in balsam. 



The sections are mounted in balsam directly from the deparaffining 

 xylene. No alcohol is used unless it is necessary to remove crystals 

 of mercuric chlorid (§ 576, 654). 



Complete Series of Embryos and Small Animals in the Three 

 Cardinal Planes, — Transections ; Sagittal Sections; 

 Frontal Sections 



§ 656. Serial sections of entire animals. — With improvement in 

 means for making thin sections of objects, the long desired ability to 

 see the entire organis-m in complete series is now easily realized. 

 What was formerly determined with so much difficulty in dissecting 

 embryos can now be attained with ease in a complete series. It is 

 almost too .easy, and with a lively imagination structural arrangements 

 are described and depicted which never actually existed in the animals 

 or embryos themselves. It is so difficult for most people to add the 

 third dimension accurately when w r orking with flat specimens that it 

 is now appreciated that the older workers had a great advantage in 

 dissecting the entire animal or embryo because they were there deal- 

 ing with an obviously three-dimensional object and true relations in 

 space were seen. There is now a wholesome tendency toward the 

 retention of the advantages of dissection of entire forms with the 

 advantages of serial sections. Hence embryos are now dissected 

 entire almost as much as in the old days, and enlarged models of the 



