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Anopheles rossi. The comparatively, high percentage of infections 

 observed by the author in the brackish water type, var. indefinitus, 

 would bring this form under suspicion, although sporozoites are appa- 

 rently not readily formed. Epidemiological evidence in the coast 

 regions of the Federated Malay States is at fault, since this type of 

 A. rossi is there so commonly associated with A. ludlowi and A. um- 

 brosus, both known carriers. The var. indefinitus collected in fresh 

 water shows a low degree of susceptibility to experimental infection 

 and but little tendency to formation of sporozoites. Neither experi- 

 mental nor epidemiological evidence indicates that this species is an 

 important carrier. The typical Anopheles rossi, Giles, of Malaya, 

 shows a comparatively high percentage of infections in laboratory 

 experiments, and sporozoites are readily formed. Further, as shown 

 in the second part of this paper, this type is capable of infecting man 

 under experimental conditions. Epidemiological evidence from other 

 countries, India in particular, indicates that A. rossi, Giles, is rarely, 

 if ever, a transmitter of malaria. But, as stated in the earlier part 

 of this paper, there is some evidence that the typical form of Malaya 

 may differ, biologically at least, from A. rossi, Giles, of India. Cer- 

 tainly the local type is easily infected experimentally, while the Indian 

 type is reported to be rather refractory. It is difficult to get satis- 

 factory epidemiological evidence in Malaya in regard to the type 

 form, since it is there commonly associated with A. ftdiginosus, 

 A. aconitus, and other potential carriers. In one or two instances 

 the author has found the larva of the typical form in the same part 

 of a lake in which A. maculatus and A. karwari were found. The 

 immediate vicinity of a certain extensive breeding place of the typical 

 form near Kuala Lumpur was not particularly malarious, but the 

 people in the vicinity, chiefly Chinese, were in the habit of protecting 

 themselves by means of bed nets. In another group of houses half 

 a kilometre away and situated near a breeding place of A. tnacvlatus 

 the people protected themselves in a similar way and were compara- 

 tively free from malaria. In both cases the population was relatively 

 stable, and possibly the introduction of a susceptible and less well- 

 protected group of people into either place might be followed by an 

 outbreak of malaria. The typical form showed a marked avidity for 

 blood in feeding experiments, and it is known to frequent dwellings. 

 These characteristics, taken in connection with the experimental 

 evidence, would bring this type under suspicion. 



Anopheles unibrosas. The evidence obtained in these experiments, 

 both in regard to the artificially and naturally infected insects, would 

 confirm Watson's conclusion that A. umbrosus is an important carrier 

 in Malaya. The susceptibility of this species under experimental 

 conditions is relatively low, but it may breed in immense numbers, 

 and evidence from laboratory experiments, as well as from the con- 

 dition of adults caught in nature, indicates that it is a relatively long- 

 lived species. No exact experiments were made as to its power of 

 flight, but adults were often found in considerable numbers at some 

 distance from breeding places, so that it is probable that A. umbrosus 

 is a strong flier. 



Anopheles aconitus. Stanton and James have recorded natural 

 and artificial infection of this species. There were but small numbers 

 in the author's experimental series, but the percentage of infections 



