in Dictyota dichotoma. 165 
(1 drop being about one-twentieth of a cc.) of the two per 
cent, osmic acid were added to ten cubic centimetres of 
chromic acid and about one-half cubic centimetre of glacial 
acetic acid. One drop of the two per cent, osmic acid proved 
sufficient in some cases to give good results. The formula 
would then be as follows :— 
1 °/ o chromic acid (in sea water) . 10 cc. 
2°/ 0 osmic acid 1 to 3 drops (1 drop = *050:.) 
Glacial acetic acid . . . . *5 cc. 
It was upon material fixed in this last-named solution that 
the results of my preliminary paper were obtained. 
Pieces of the plant, on being thrown into these fluids, 
became dark almost at once, but after a short time the dark 
colour of the thallus disappeared owing to the oxidation 
caused by the chromic acid. 
Since it was impossible to make in any way an exhaustive 
study during my stay at the Station in Naples, material fixed 
in the above solutions, and also in various strengths of 
Vom Rath’s platinum-chloride-osmic-acetic acid, was brought 
gradually into seventy per cent, alcohol, where it lay until 
ready for use, which was during the following December and 
January, 1899. 
In the course of investigation, material which had been 
fixed in the solutions A and B previously mentioned, gave, 
to my agreeable surprise, excellent results, for many pre¬ 
parations made from such material left little to be desired. 
Vom Rath’s fluid gave less satisfactory results. 
In thin sections the blackening was readily removed by 
allowing the slide to remain for a short time in a bath of 
alcohol and hydrogen peroxide (70 cc. of 80 °/ 0 alcohol and 
30 cc. of hydrogen peroxide). 
Material fixed in solutions weak in osmic acid gave good 
results also after lying in the seventy per cent, alcohol for the 
time mentioned, but differential staining was more difficult 
and less satisfactory. The radiations and spindle-fibres 
retain the stain with less avidity, consequently the finer 
