109 
when the pollution is over a year and a half or 2 years old, bacillus 
cloace was the only coliform organism that could be isolaied. 
The presence of this organism in large numbers in any water 
usually, but not invariably, indicates that it comes from a lake 
that is getting low or a river that is drying up. It has already 
been pointed out that during the hot weather the num- 
ber of bacillus cloace appears to increase in the feces of 
human beings and animals, and in water-supplies simulta- 
neously ; the fact that there is no rain falling shows that the 
increase in the water-supplies is not due to the increase in 
faeces. Were this the case, the type of pollution present in 
the water-supplies would have all the appearances of recent 
pollution, viz., usual fecal arrangement of bacilli, and the 
closeness of the acid and gas line in glucose and lactose; but 
this is not noticed at this time of year, so that the great pre- 
valence of cloace in water is not due to this cause. Inspec- 
tion of the lakes in question shows that pollution does not 
take place when no rain is falling. 
The Vesiculosus and Grunthal Group. 
We have already shown that bacillus cloace is essentially 
an organism which belongs to the bottom of lakes and to 
river sand bacillus; one organism of the Grunthal-vesicu- 
losus group is also extremely resistant ina somewhat different 
way. In all probability bacillus vesiculosus is the resistant 
member of this little group, but as all species give negative 
results in all the sugars, it is extremely difficult in practice to 
decide between the various species. After considerable 
pollution has taken place, and the lactis erogenes bacilli have 
begun to disappear, usually the only organism that can be 
obtained from the surface of a lake is either bacillus Grunthal 
or bacillus vesiculosus. The bacillus is particularly common 
in surface samples obtained from settling tanks, storage 
reservoirs and rivers in the hot weather ; it usually is common 
after the disappearance of the lactis erogenes and before 
the water has got low enough to reach the cloace. It isthe 
common bacillus of a well sunned full reservoir. The sunlight 
experiments also demonstrate the fact that it is in reality a 
