the Yeast Plant. 
7 i 
a small amount of phosphorus present, owing to the fact that it is composed 
largely of the molybdic oxide and contains only 3*1 per cent, of P 2 0 5 . It 
is sufficiently abundant in a cell to be distinctly visible under the micro¬ 
scope, but the yellow precipitate is often masked by the yellow coloration 
produced in the tissues by the action of the nitric acid, and consequently no 
differentiation is visible. Macallum (’ 98 ) has, however, devised a method 
by which this difficulty is overcome. Molybdic oxide, when acted upon by 
reducing agents, such as pyrogallol, stannous chloride, and zinc chloride, 
is changed in colour from white to green, blue or black, according to 
the reagent employed. The subsequent treatment of cells, which have 
been acted upon by the nitric ammonium molybdate solution, with one 
of these, therefore, produces a dark coloration in those parts in which the 
precipitate has been formed. As, however, both pyrogallol and stannous 
chloride produce a similar effect upon ammonium molybdate itself, neither of 
these is suitable, since, if the nitric ammonium molybdate solution is not 
properly washed out, which appears to be difficult to accomplish in many 
cases, they cause a coloration in the tissues as well as in the phosphorus- 
containing elements. Zinc chloride does not give any colour to the 
ammonium molybdate, but its action upon the precipitate is too slow 
for practical purposes. Macallum (’ 98 , ’ 99 ) found, however, that phenyl- 
hydrazin hydrochloride in 1-4 per cent, solution in water gives a deep 
green coloration of the phospho-molybdate precipitate, but does not cause 
any coloration of the ammonium molybdate. The nuclein-containing 
elements are in consequence clearly differentiated. Macallum (’ 99 ) used 
this method to demonstrate the presence of organic phosphorus in yeast 
cells, and found that the corpuscle (nucleolus) is rich in it, that the wall of 
the vacuole in contact with the corpuscle gives a distinct reaction for 
it, and especially at times the granules contained within the vacuole. We 
have found the method extremely useful in determining the distribution of 
the nuclear constituents of the cell, and our observations confirm those 
of Macallum, and afford some additional evidence for our views as to the 
nature of the yeast nucleus. 
The best results were obtained with fixed cells (alcohol or iodine), the 
distortion in the case of fresh material being so great as to preclude the 
recognition of definite reactions in particular parts of the cell. The cells 
are treated for ten minutes to forty-eight hours with a nitric acid solution 
of ammonium molybdate, which produces the yellow coloration in those 
parts which contain phosphorus. They are then washed and placed in a 
freshly made 1-4 per cent, solution of phenyl-hydrazin hydrochloride in 
water. In the course of two or three minutes the phospho-molybdate 
becomes reduced to the green oxide, and those parts of the cell in which it 
is contained can be easily differentiated by their colour, which varies from 
light to dark green (Figs. 117-30), from the other parts of the cell, which 
