466 MEDICAL ENTOMOLOGY 



If the number of fleas found naturally on each host is small, all 

 the fleas from several hosts should be transferred to one experimental 

 animal, preferably a young one. This is best done by chloroforming 

 the hosts, and removing the fleas by means of a fine comb. If they 

 are placed in the cage with the future host they will pass on to it 

 as soon as they recover from the anaesthetic. 



Minchin and Thompson, in their experiments with the rat flea as 

 a transmitter of Trypanosoma lewisi, in some of which only one flea 



was used for each animal, used ' specially constructed 

 Manipulation of , ... r ,. , , . 



single Fleas cages, each consisting of a tin cylinder, 6 m. in 



'diameter, 10 in. in height; the bottom is closed in 

 1 with tin, the top with a tightly fitting tin cover, which has an opening 

 ' sufficiently wide to admit air for the rat, but barred doubly with both 

 ' wire gauze and finely meshed cloth gauze, the former to prevent the 

 ' rat forcing its way out, the latter to make it flea proof.' Some 

 sawdust was placed at the bottom of the cage, and the rat kept in it 

 during the period of the experiment. A single flea could be recovered 

 from the rat, or from the sawdust. 



Noller, in his elaborate and exact experiments on the transmission 

 of Trypanosoma lewisi by the dog flea, adopted the method in use by 

 keepers of performing fleas. The flea is enclosed in a loop of fine 

 silver wire, '1 mm. thick, passed around its thorax between the second 

 and third pairs of legs, the free portion of the wire being twisted into 

 a spiral to serve for a handle. The fleas are thus secured at the 

 commencement of the experiment, and remain under perfect control 

 while they are fed. In the intervals between feeds they are kept, 

 still fastened to their wire handles, in open Petri dishes, between two 

 layers of cotton wool. 



The cages used by the Indian Plague Commission for the demon- 

 stration of transmission of plague from rat to rat were constructed as 

 follows. A wire cage about 12 cm. in diameter and about 8 cm. high, 

 having a mesh of '1 mm., contained the rat. This was attached below to a 

 tray containing sand or dry earth. The upper side was completed by a 

 cylinder of metal, 15 cm. high and 9 cm. in diameter, the upper end of 

 which was covered with a lid. Two of these cages were enclosed in a glass 

 box, the top of the whole being covered with fine muslin, of a mesh 

 through which fleas could not penetrate. The top of the lid, which had 

 an aperture for the supply of air to the rat, was also covered with muslin. 

 In this way the two rats could not come in contact with one another, nor 

 with the urine or faeces, but fleas could pass readily through the wire-work 



