87 
of the Genus Hillhousia. 
to mere specks are found lying in the threads of the protoplasmic reticulum. 
They are of a dull red colour and rather refractive in appearance. They 
remain in the protoplasm when the organisms are dried and re-irrigated with 
water, but if left for some days freely exposed to the air they slowly 
disappear. 
They are soluble in hot potassium hydrate, in potassium cyanide, 
in carbon bisulphide, in chloroform, in strong nitric acid, and in glacial 
acetic acid. They are unaffected by the reagents that dissolve the globules 
of calcium carbonate. 
If strong picric acid is added to organisms previously cleared of calcium 
carbonate, and subsequently washed thoroughly in water, the sulphur grains 
tend to run together and to become crystalline. 
If the organisms are mounted on a slide in 40 per cent, formalin, 
the sulphur grains slowly crystallize in the course of a few weeks. If 
mounted in dilute acetic acid crystallization takes place in a few hours. 
The crystals are typical double pyramidal crystals of sulphur ‘of a yellow 
colour (Fig. 7). 
If individuals containing sulphur grains are treated with warm potas- 
sium cyanide and ferric chloride, a deep red coloration is produced. 
Organisms without sulphur grains do not produce this coloration. 
When a quantity of organisms containing sulphur grains are burned on 
platinum foil, a very distinct odour of sulphur dioxide is noticed. 
These experiments show that the reddish grains are of sulphur. The 
sulphur grains of Beggiatoa are precisely similar, in appearance and in their 
behaviour to reagents, to those of Hillhousia . 
Conditions necessary for Healthy Existence. 
These lime-sulphur Bacteria are easily affected by slight changes 
in their environment. In order to remain in a healthy condition they 
require a sufficiency of lime-salts, sulphuretted hydrogen, and oxygen. 
Hillhousia has been kept in a healthy condition for more than nine 
months in a glass dish six inches in diameter and two inches deep. The 
mud in which the organisms normally live was placed in tap-water in the 
dish, and water was added to replace that lost by evaporation. It was 
found necessary to stir up the mud frequently in order to get rid of 
the excess of sulphuretted hydrogen and to aerate the water. 
If fresh water is allowed to run through a collection the organisms 
lose their sulphur within forty-eight hours. If the mud is then left 
undisturbed so that sulphuretted hydrogen can accumulate, the sulphur 
grains reappear. The addition of chemically prepared sulphuretted hydro- 
gen to organisms removed from the mud and placed in fresh water also 
causes the sulphur grains to reappear, provided that the water has been 
