282 KATHARINE FOOTE AND E. C. STROBELL. 



serial sections were impossible. We also tried Biitschli's method 

 of painting each section with a thin layer of colloiden. In this 

 way Butschli obtained satisfactory sections less than i // thick, 

 but we failed to get like results. 



We were convinced that the difficulties were not due to mechan- 

 ical defects in the microtomes, for we were able to cut sections 3, 

 2 and even I // with almost every microtome we have tried. But 

 in these thin sections, the perfect contour of the eggs was de- 

 stroyed, their diameter in some cases being reduced more than 

 one half. This we demonstrated by cutting a series of sections, 

 the first half dozen 10 ft., the next half dozen 5 fi, then 4, 3, 2 

 and I IJL. Comparing the last sections of the series with the 10 // 

 section showed how much the structure of the egg was sacrificed 

 to the thin sections, and convinced us of the necessity of devising 

 some special method to harden the paraffine in order to secure 

 thin sections in everyway up to the standard of the 10 // section. 



Experimenting with a block of pure paraffine less than one 

 eighth of an inch square (without any imbedded object) and 

 setting the microtome at 3 ft, we gradually lowered the surround- 

 ing temperature until each section of the paraffine maintained the 

 exact size of the original block. 



The text-figure on page 283 illustrates the freezer we finally 

 designed to enable us to cut serial sections of I y 2 to 2 l / 2 [i at a 

 temperature about 25 Fahrenheit. The work table, on which 

 the freezer is operated, is placed close to a north window, and on 

 the table we put a heavy cotton pad, covering this with a heavy 

 rubber sheet. Then the microtome (Thoma in our case) is set in 

 place on the rubber sheet. Near the microtome we arrange the 

 wooden object carriers, each with its subject ready for final cut- 

 ting ; the necessary number of clean slides and boxes (with 

 close covers) just large enough to hold a slide. 1 Then the 

 freezer is put in place over the microtome, the work table form- 

 ing the bottom of the operating compartment D. The ice cham- 

 ber B is then packed with alternate layers of cracked ice and salt, 

 the corks tied securely in the hand holes H, and a rubber tube 

 fitted over the drain tube M with the free end in a pail under the 



1 We use for this purpose the shallow tin boxes formerly made for typewriter 

 ribbons. 



