400 THE AMERICAN MONTHLY [Nov. 



per cent solution of the methylen blue into the blood ves- 

 sels for the central nervous system and by immersing- 

 small pieces of nerve tissue in a weak solution of the stain 

 for the sense organs. 



The leng-th of time required for the intra vitam staining- 

 varied widely, annelids requiring 4-5 hours, while dog-fish 

 only require X-]/?. hours, either by injection or by immers- 

 ing- the tissiie in the stain. 



When small transparent pieces of tissue were to be 

 examined, they were fixed in a saturated solution of picrate 

 of ammonia in distilled water from 2-4 hours and were 

 then mounted in a mixture of equal parts of pure glycerine 

 and distilled water to which a small quantity of picrate of 

 ammonia is added. When opaque or large pieces were 

 fixed in this way they were sectioned by the freezing- 

 method. After fixing- in the picrate of ammonia, the tissue 

 was placed in a saturated solution of sugar for one hour 

 and was then transferred to a piece of blotting paper to 

 remove the syrup from its surface. It was then placed 

 in a thick solution of gum arabic for fifteen minutes and 

 then transferred to the plate of the freezing- microtome, 

 where it was frozen by means of liquid carbonic acid. The 

 sections were mounted in dilute glycerine as in the other 

 case. The principal advantage of this method is its rapid- 

 ity, but neither serial sections nor those of equal thickness 

 can be obtained. 



In order to obtain serial sections by the parafifine method, 

 the tissues were fixed in Berthe's Fluid. 



FOR VERTEBRATES. 



Molybdate of ammonia, 1 g-ram. 

 Distilled water, 10 c. c. 

 Hydrochloric acid, 1 drop. 

 Peroxide of Hydrog-en, 1 c. c. 



FOR INVERTEBRATES. 



Molybdate of ammonia, 1 gram. 

 Distilled water, 10 c. c. 

 Peroxide of Hydrogen, >^ c. c. 

 A different formula is used for tissues of invertebrates. 



