326 TRYPANOSOMA RHODESIENSE [CH. 



B 119, shewn to be non-infective by feeding upon clean mon- 

 keys, were fed for three days on a rhodesiense-iniected guinea- 

 pig. Each batch was then fed on a healthy monkey until the 

 fortieth day, the mean temperature being 59° F. Neither 

 monkey became infected. The 42 flies remaining of batch A 

 were placed in the incubator at 85° F., and the 58 flies of batch 

 B were left at laboratory temperature. Of the batch A flies, 

 on the 43rd day only six were alive. From the 41st to the 47th 

 day the flies of batch A were fed on a monkey (which died) ; 

 from the 48th day on a rat. The rat became infected, shewing 

 that batch A contained an infective fly on the 48th day, eight 

 days after being placed in the incubator. The four flies still 

 alive on the 53rd daj^ were fed on four clean rats, three of which 

 became infected. 



On the 6ist day the 38 flies of batch B, which had then 

 failed to infect the monkey, were put in the incubator at 83° F., 

 and from that day till the 75th were fed on a healthy monkey. 

 The animal unfortunately died. All the flies were dissected as 

 they died. One was found to harbour trypanosomes in the 

 salivary glands and gut, and animals inoculated with the con- 

 tents became infected. In the first part of the experiment the 

 relative humidity in the incubator was 36 per cent., in the 

 second, 72 per cent." 



This experiment clearly shews that at a comparatively low 

 temperature the early stages of the trypanosomes may persist 

 in the alimentary canal of the fly for sixty days, but that for 

 the completion of the cycle of development a higher tempera- 

 ture is required (75° — 85'' F.). The necessity of a certain degree 

 of heat, before the fly can become infective, explains why 

 Kleine was unable to transmit T. gambiense by G. morsitans on 

 Lake Victoria, where the temperature is not high enough. 



The life cycle of T. rhodesiense within the tsetse-fly has not 

 been thoroughly worked out, but seems to present many points 

 of resemblance to that of T. gambiense in G. palpalis. The 

 trypanosomes first become established in the intestine and in 

 every case the salivary glands are invaded before the fly 

 becomes infective. The manner in which the glands become 

 infected is uncertain, but it is apparently secondary to the 



