C. Strickland and N. H. Swellengrerel 
441 
We had positive results in 20 experiments and as one flea at least 
in each experiment must have been infective, at least 20 must have 
been infective, i.e. about 2 “/o of the total number used. 
Therefore at least 2 “/o and not more than 20 "/o of our fleas were 
infective. 
We would like here to add the results of flea infection experiments 
which one of us (C. S.) obtained before the publication of Minchin and 
Thomson had appeared, since they concerned cases of what may be 
regarded as ‘distant transmission’ observed in January, 1909. 
Experiment 1. About 20 fleas of two species {G. fasciatus and C. agyrtes) from 
an infected wild rat were placed u 2 Jon a tame white Rat XV. Four days later 
Rat XV died and about six fleas from it were then ^flaced on a ‘clean’ Rat XI. Two 
days later this rat died, and the fleas from it were jdaced on Rat XVII which 
became infected in six to ten days. The fleas were therefore infective six days 
after taking them from the infected rat. 
Experiment 2. 17 fleas from an infected wild rat wei’e put on a ‘ clean ’ rat for 
12 days when nine were recovered and 2 >ut on a second ‘clean’ rat. This became 
infected in eight days. These fleas were therefore infective 12 days after coming 
from the infected rat. The first ‘ clean ’ rat did not become infected. 
The result of the following experiment can be interpreted in the 
■way indicated in the second paragraph of this section (distant continuous 
transmission). 
Experiment 3. 15 fleas taken from an infected rat were placed immediately on 
a ‘clean’ white Rat XX. In three days four were recovered and ^nit on Rat a ; 
similarly after two and one days the fleas were ^rlaced in succession on Rats h and c. 
All four rats became infected. 
The following experiments also prove distant transmission. 
Experiment 4. Rat 5 was filaced in a box containing fleas which 14 days 
2 )reviously had fed on an infected rat. Rat 5 became infected. 
Experiment 5. Rat d was used to feed fleas upon 12 days after they had fed on 
an infected rat. Rat d became infected. 
Experiment 6. Fleas from an infected rat were jrlaced on a ‘ clean ’ Rat e seven 
days after they had fed upon the infected I’at. Rat e became infected. 
Experiment 1. Fleas from an infected rat A were ^rlaced on a ‘ clean ’ rat B 
17 days after they had fed on the infected animal A. Rat B became infected. 
Experiment 8. A rat Dttt was irlaced in a flea box from which an infected rat 
had been taken three weeks jjreviously. Rat Dttt became infected in seven days. 
Experiment 9. Fleas were fed on an infected animal for an hour and were then 
fed daily on a series of ‘clean’ animals from the 4th—33rd day, but none of 
them became infected. On the 34th day the fleas were 2 )ut on Rat C which became 
infected. 
