XIII, B, 1 



Barber: The Transmission of Malaria 



25 



pupae and subsequently bred out in the laboratory. Mosquitoes 

 collected as adults are apparently less avid of blood than those 

 from the other source, but this cannot wholly explain the differ- 

 ence in infectivity. In some lots insects taken in the imago stage 

 were known to have taken blood, and but a small proportion be- 

 came infected. A record was kept of some series of insects 

 caught in the imago stage with regard to the proportion taking 

 blood at one exposure. In 5 lots of umbrosus, 44 out of 87 once 

 exposed took blood; in rossi var. indefinitus, brackish water, 15 

 out of 20 ; in kochi, 7 out of 8. As a routine, material taken as 

 adults was kept one or two days before exposure to a carrier, 

 in order that they might have time to digest the blood already 

 present in the gut. They were then, as a rule, exposed several 

 times ; it is probable that the majority of them took blood on re- 

 peated exposures. Whatever the explanation, there is evidence 

 that such insects are less susceptible to infection, and they cer- 

 tainly afford less favorable material for infection experiments. 

 The periods of time intervening between exposure to gamete 

 carriers and dissection are summarized in Table XIII. Only 

 controlled series are included. Since the same cage was some- 

 times exposed on several succeeding days, the day groups are 

 made large, so as to include as large a proportion as possible 

 of the dissections. In lots exposed to carriers on a series of days 

 one cannot, of course, determine exactly the period intervening 

 between actual infection and dissection. 



Table XIII. — Periods intervening beUveen feeding and dissection. 



Days. 



Three to six 



Seven to nine 



Ten to fifteen 



Fifteen and one-half to twenty 



Twenty-one to twenty-eight and one-half 



Total - — 



Dis- 

 sected. 



258 



134 



261 



87 



13 



743 



Positive. 



Per cent. 

 27.9 

 23.9 

 3-3.1 

 19.5 

 30.8 



29.5 



Specimens were often dissected in the earlier day periods in 

 order to determine the percentage of gut infections. Where 

 there was evidence of infection in a cage, further dissections 

 were often postponed to a time when sporozoites might be found. 

 This explains the relative fewness of dissection in the 7- to 

 9-day group as compared with the 3- to 6- and 10- to 15-day 

 groups. 



