276 Messrs. Minchin and Thomson. Transmission of [Jan, 7,. 



no difficulty in obtaining 200 fleas from the breeding cages for an experiment 

 when required. The fleas are kept alive in the cages by being fed on non- 

 infected healthy tame rats. 



Although it is not known whether any of the rats on which the original 

 50 fleas were caught were infected with T. leivisi or not, it is quite certain 

 that the stock of fleas in our breeding cages is free from infection, since not 

 one of tlie many non-infected rats used for feeding them has ever become 

 infected. We are indebted to the Hon. N. C. Rothschild for kindly identi- 

 fying the genus and species of our fleas as Cemtophylhis fasciahis. 



In preparing for each of these experiments, the first step was to collect a 

 sufficient number of fleas, usually about 200, from the breeding cages. These 

 fleas were then exposed to infection by being put, together with a heavily- 

 infected rat, into a tin cage specially constructed to facilitate the recovery 

 of the fleas. The infected rat itself was ascertained to be free from fleas 

 before it was put into the tin cage ; and the fleas from the breeding cages 

 were left with it in this cage for a known period of time. At the end of this 

 period as many as could be recovered from the infected rat and from the tin 

 cage were used to colonise a freshly prepared cage, constructed on the model 

 used by the Indian Plague Commission for their experiments on rats and 

 fleas.* This cage, which we will call Cage X, was carefully cleaned and dis- 

 infected before being used for the experiment, and into it a healthy, non- 

 infected rat (Eat XI) was now introduced, togetlier with the fleas collected 

 from the tin cage already mentioned. Three or four days later, or when 

 under the special conditions a sufficient time had elapsed to ensure that any 

 flea that survived must have fed on Eat X 1, this rat was removed from 

 Cage X, and was carefully cleaned from fleas by the aid of chlorolbrm-vapour, 

 after which it was put into a fresh cage by itself. The fleas removed from 

 Eat X 1, after they had recovered from the chloroform-vapour, were put back 

 into Cage X. Another healthy, non-infected rat (Eat X 2) was then put intO' 

 Cage X, and so on witli Eat X 3, X 4, etc. (each treated similarly to Eat X 1). 

 Each of these rats, after removal IVoni Cage X, was then examined daily or 

 every other day subsc(iucntly for trypanosomes in its blood. 



(2) Di'tailcd Account. 

 lO.xpei iiiK'iit A. 



4/10/09. — 200 HoaH taki'ii from llio breeding c;ige were i)ut into tlie speeial tin cage 

 together with a heavily-infected tame rat showing many trypanosomes in its 

 blood. 



8/10/09. — 44 fleas recovered from the above-mentioned cage were ])ut into a freshly- 

 piepared flea-proof cage (Cage A), together with a clean, healthy rat (liat A 1). 



* .See 'Jouiiial of Hygiene,' vol. G, l!)Of), ]). 4.35, ])1. 4. 



