- 1900-1901.] Experiments on the Growth of Yeast. 215 
man, one of the audience asked naively what effect the 
parasite had on the mosquito? There was a little laugh 
_ when Major Ross answered that he had not studied that point. 
It was, notwithstanding, a very philosophical question. 
Much has appeared lately in the newspapers about the 
poisoning of beer-drinkers by arsenic contained in the beer, 
but hardly any one asks the far more significant question, 
What effect has a poison like arsenic on a simple growing cell 
like yeast? It is one of a number of questions of extreme 
biological interest, as we shall presently show. For field 
_ naturalists—that is, people who occupy themselves with nature 
_ studies—there is no way of advancing these studies like 
_ trying to grow organisms in new and definite conditions. 
_ Bonnier took plants of the plain far up the Alps or the 
Bie rrences and planted them in a garden there, and they 
assumed an alpine form. A Jerusalem artichoke, for example, 
ceased to have a tall stem, its leaves became crowded together 
and hairy, and lay close to the ground. Niigeli grew hawk- 
-weeds—of all plants those in which species are most difficult 
j to distinguish, He had 2500 in the Botanic Gardens at 
Munich. He studied them for thirteen years to see if changes 
arising from culture were permanent, and he got negative 
results. Maupas grew rotifers at definite temperatures, and 
_ found how at a higher temperature numbers of male eggs were 
produced, like drones amongst bees. 
In order to test the effect of arsenious oxide on the growth 
of yeast, it was necessary to ascertain the amount of glucose 
converted into alcohol in solutions of definite strength and 
containing known quantities of arsenious oxide. For this pur- 
pose the following solutions were prepared: (1) a solution of 
commercial glucose containing 125 grammes in one litre of 
water, this strength being such that 80 cc. of the solution 
mixed with 20 c.c. of water gave a 10 per cent solution of 
glucose ; (2) ten solutions of arsenious oxide of such strengths 
that 20 c.c. added to 80 cc. of water would yield solutions 
_ containing the following proportions of arsenious oxide: (A) 1 
"in 500; (B) 1 in 1000; (C) 1 in 2500; (D) 1 in 5000; 
(EZ) 1 in 10,000; (F) 1 in 20,000; (G) 1 in 30,000; (H)1 
in 40,000; (I) 1 in 50,000; and (K) 1 in 60,000. 
_ The mode of conducting the experiments had next to be 
Seoningnar 
