BRIEFER ARTICLES. 
THE CELLOIDIN METHOD WITH HARD TISSUES. 
Tue following celloidin method, developed and perfected by Dr. E. 
C. Jeffrey, has been incompletely described at second or third-hand 
elsewhere,’ but is here published in full for the first time, in response . 
to numerous inquiries from persons interested in the photomicrography 
of plant tissues, and in the preparation of large numbers of uniform 
sections for class use. This method has been employed in the labora- 
tories of plant morphology of Harvard University for two years, and 
when judiciously applied it is found to leave practically nothing to be 
desired. The hardest tissues may be cut as thin as 5 or less, without 
difficulty,if they are first properly treated, and the sections thus obtained 
are perfectly adapted to photographic requirements. Briefly stated, 
the method as specialized for the study of wood and other objects con- 
taining skeletal tissues, is as follows: 
I. Preparation of material lf wood is to be studied, it should be 
cut up into cubical blocks, in such a way that the faces represent accu- 
rate transverse, radial, and tangential sections. The best results are 
obtained from cubic blocks of not more than 1“, though much larger 
ones may be used if the time of treatment be proportionately increased. 
Material other than wood should be cut in similarly small pieces, and 
in such a way as to afford the desired plane of section. If the material 
is dead and dry, the pieces should be repeatedly boiled in water and 
cooled, in order to remove the air. It is well to pump out the remain- 
ing air with a good vacuum pump. In case living material is to be 
studied, the protoplasm may be killed and fixed by placing the blocks 
directly in the following solution : 
Mercuric chloride, saturated solution, in 30% alcohol - - - 3 parts 
Picric acid, saturated solution, in 30% alcohol - - I part 
After twenty-four hours this solution is to be washed out by passing 
the blocks through alcohols of grades 40, 50, 60, 70, and 80 per cent. 
Twelve to twenty-four hours should be allowed for each change of 
alcohol, and the 80 per cent. alcohol should have enough iodin solu- 
! CHAMBERLAIN, C. J., Methods in plant histology, p. 55; also MILLER, C. H.,On 
embedding in celloidin. Jour. Applied Micr. 6: 2253-2254. 1903. 
456 [JUNE 
