50 
Bilharzicisis 
Observations on Infested Snails of Bullinu,s and Planorbis 
Genera. 
Under laboratory conditions we have frequently found that infested snails 
die more rapidly than normal ones, even when great care is taken regarding 
feeding and supply of fresh water, etc. If out of a batch of such snails 100 are 
dissected at weekly intervals, the percentage of those infested is found to 
steadily decrease. Even under laboratory conditions however, and notwith¬ 
standing a heavy infestation, certain snails have been observed to produce 
cercariae for many weeks. It seems probable, therefore, under natural con¬ 
ditions that infested snails may survive for long periods. 
We have observed very definite macroscopic and microscopic change^ in 
infested snails. 
The appearance of the infested snail. After a little experience the infested 
snail can be recognised by the naked eye, by certain stigmata; this more 
generally applies to Planorbis. The shell itself is glossy, smooth, and shiny 
in appearance, and is almost invariably friable—this point alone is a good 
indication of probable infestation. 
The infested snails are, in the majority of cases, fully adult and the herma¬ 
phrodite gland contains ripe ova, though occasionally half-grown specimens 
have been found infested. In those heavily infested, the golden-yellow colour, 
so characteristic of the liver in this condition, may be seen appearing through 
the shell wall itself. The organ itself is swollen and friable; it may be either 
ochre, bright yellow, or greenish brown in colour, and abundantly speckled 
with gray spots. Generally the right lobe of the liver contains the greater 
number of cercariae, as does also the hermaphrodite gland, which lies midway 
between the two hepatic lobes. The fatty degeneration of the liver, as it would 
appear to be, is not brought about exclusively by the bilharzia cercariae, but 
occurs also in snails infested with the cercariae figured in Plate IV, fig. 5. 
On microscopic examination deposits of sporocysts and cercariae in the 
interacinous tissue are to be noted. These displace the acini of the glands and 
cause pressure atrophy of the parenchyma; in heavily infected livers, fully 50 
per cent, of the total mass consists of sporocysts and cercariae (PI. V, fig. 1). 
Confirmatory proof that cercariae obtained from.\ Planorbis develop only into 
adult worms hairing the morphology of S. mansoni, while those obtained 
from, Bullinus develop only into adult worms having the morphology of 
S. haematobium. 
Monkeys were infested in the following way. A snail's liver, which was 
found microscopically to contain a large number of mature cercariae, was placed 
on a shaved area of the leg or abdomen of the monkey, and was permitted 
to remain in contact with the skin for from five to twenty minutes. 
After an average period of six weeks, these monkeys became very thin and 
