516 Reed.— The Vahte of Certain Nutritive Elements 
the living cells to be examined were placed in o-i per cent, ammonium 
hydroxide for one hour, then into a io per cent, solution of potassium 
ferrocyanide containing 5 per cent, acetic acid. The mixture was always 
freshly prepared by mixing equal quantities of 20 per cent, potassium 
ferrocyanide, and 10 per cent, acetic acid. The cells remained in this 
mixture for twelve hours, and were then washed in distilled water until the 
washings no longer gave a blue colour with ferric chloride. They were 
then placed in a 3 per cent, solution of ferric chloride for twelve hours. 
After this treatment the albuminous materials were coloured deep blue. 
In testing for fats I did not rely upon the usual application of one per 
cent, osmic acid. The black colour which appears when dilute osmic acid 
is applied to fats follows from the reduction of osmic acid (osmium tetroxide) 
to metallic osmium. This reduction is accomplished by the unsaturated 
series of fats represented by olein and oleic acid. Wlassak (’ 98 ) has shown 
that the same reduction of osmic acid may be accomplished by lecithin. 
This may happen by virtue of the fact that lecithin contains the oleic acid 
group, lecithin being in fact the stearic-oleic-glycero-phosphate of cholin, 
and in the presence of water some oleic acid is probably formed. This is 
in accord with Wlassak’s observation that pure lecithin readily stains with 
osmic acid if previously kept for a time in water. Wlassak also pointed 
out that while osmic acid stains both fat and lecithin, the method of 
Marchi stains only the fat. This is because the lecithin loses its power 
of reducing osmic acid if it is kept for some time in a solution of potassium 
bichromate, while olein does not. Halliburton and Mott (’ 02 ) have given 
this subject further study, and point out the probability that when potassium 
bichromate acts upon lecithin it oxidizes the oleic group. When osmic 
acid is applied to such a preparation it is not reduced, and hence the 
preparation does not blacken. In practice I found it best to put the plant 
tissues directly into Erlicki’s fluid, and allow them to * harden ’ five to seven 
days at room temperature. Subsequently they were treated with one per 
cent, osmic acid. 
Although no extensive experimentation was attempted with stains and 
mordants, a few were of sufficient merit to deserve mention. 
Excellent results in staining Algae were obtained with iron-alum-haema- 
toxylin and with safranin. The safranin stain was much improved when 
the filaments were previously mordanted in potassium permanganate 
according to the method of Henneguy. 
In staining the protonema of mosses and the prothalli of ferns, the best 
results were obtained by using a modification of Hartog’s nigrosin and 
carmin method. 1 
1 The process is as follows (i) The living material is put for forty minutes in 50 per cent, 
alcohol containing glacial acetic acid equivalent to two per cent, of the entire volume. (2) After 
briefly rinsing in 50 per cent, alcohol, the material is stained thirty to forty minutes in Grenacher’s 
