752 The American Naturalist. [August, 
Spirogyra with the hay bacillus may be used to show that it is not the 
colorless protoplasm, nucleus, cell sap, or cell wall, but only the chro- 
mophyll bodies that give off oxygen. Light thrown on a chlorophyll 
band of Spirogyra causes the bacteria to swarm to it, while light thrown 
on any other part of the cell causes no crowding or movement of the 
bacteria. Light thrown on a chlorophyll band, after being passed 
through an alcoholic solution of chlorophyll derived from Spirogyra, 
caused no crowding or movement of the bacteria, while light passed 
through red glass, although less intense, caused an active swarming of 
the bacteria around the illuminated part of the band. The same 
method may be used to show whether red and variously colored cells 
contain chlorophyll, and whether the chlorophyll-bearing protoplasm 
of a cell is living or dead. The author obtained some of his results 
with undetermined bacteria from the surface of slightly foul water, but 
fresh cultures of Bacillus subtilis also gave good results. Organisms 
which make only a small demand on free oxygen, such as Vibrio line- 
ola and Spirillum tenue give somewhat different results. In this case 
the motile organisms crowd around the algal spore or thread only when 
it is under the influence of feeble light. When bright light is let in, 
too much oxygen is given off, and a space is cleared around the green 
cell which widens or narrows in proportion to the varying of the light. 
With waning vigor of the chlorophyll the same results are obtained in 
bright light as with vigorous cells in feeble light, i. e., a crowding of 
the bacteria close up to the algal cell. The appended bibliography 
includes 61 titles, beginning with the year 1881, when Engelmann first 
published on this subject.—Erwin F. SMITH. 
Detection of Glukase by Auxanographic Methods. Beyer- 
inck has devised a neat method for showing that the enzym, glukase, 
first changes cooked starch into dextrine and subsequently into glucose. 
Over } the bottom of a Petri dish or similar receptacle, which part we 
will designate A, he pours a nutrient gelatine (10 per cent. gelatine ; 
$ per cent. soluble starch ; + per cent. asparagin; zs per cent. potas- 
sium phosphate) infected with Saccharomyces ellipsoideus or any other 
maltose yeast which is able to take nitrogen from asparagin, but will 
not react on dextrine. Into the other } of the dish, which we will 
designate B, he pours a nutrient gelatine infected with the same yeast 
and of identical composition except that the soluble starch is left out. 
Of course, no growth occurs in either part, because neither contains any 
carbohydrate on which this yeast can feed. A small area on A is now 
strewn with glukase powder and at some distance the same powder is 
