194 MOSQUITOES OF NORTH AMERICA 



be summarily dismissed. The suspicion of such a possibility must occur to any- 

 one who has experience with the subject and who has observed that when in the 

 months of epidemic malaria the carriers of gametes, who serve as the means of 

 infecting mosquitoes for experimental research, are in very small proportion 

 and that nevertheless the epidemic increases with great rapidity. Withal it 

 will be futile to seek the explanation of this phenomenon outside of the mosquito, 

 where alone, sooner or later, it will be found. 



Practically an Anopheles can become a transmitter in 10 to 13 days after 

 having fed. This period may be diminished under optimum conditions for the 

 vitality of the Plasmodium. It would appear from the few experiments in this 

 direction made with each species of Plasmodium that this period is variable. 

 The most favorable temperature appears to lie between 22° and 28° Centigrade. 

 Beyond these conditions the development of the parasite goes forward more 

 slowly and there are observations which show a period of more than 50 days. In 

 hot countries, during the months of greatest heat, the proportion of malignant 

 tertian to the entire number of cases of malaria may reach as high as 96 per cent. 

 After this epoch the malignant tertian decreases and is replaced in proportion 

 by the benign tertian. The quartan malaria is generally everywhere much 

 the rarest form. 



It is not rare in malarial countries to find children harboring ring-forms of 

 the parasites which are indistinguishable from Plasmodium falciparum and yet 

 these children present no symptoms of abnormal health except splenomegaly. 

 They are typical cases of imunitas non sterilans — immunes who, nevertheless, 

 are bearers of the parasites and therefore sources of infection. Do the parasites 

 lose their virulence, or are they a different species ? We have already mentioned 

 that parasites exist in every way like those of malignant tertian but which in 

 their development produce attacks of a very benign character. Some authors 

 also report two clinical types of quartan malaria, one benign, the other malig- 

 nant; however it has been impossible to differentiate the parasites micro- 

 scopically. 



Spontaneous recoveries from malaria can be observed with a certain frequency. 

 It is to this circumstance that the supposed efficacy of remedies other than 

 quinine is to be attributed. Of such remedies the only one of any value is 

 methylene blue which acts destructively upon the plasmodia, but its effect is slow 

 and in cases of acute malignant tertian it does not act with the necessary 

 rapidity and energy, as does quinine. Under certain conditions there may come 

 about the formation of races of Plasmodium resistant to quinine. 



THE SCIENTIFIC DEMONSTRATION OF THE CARRIAGE OF MALARIA. 



Before the actual demonstration of the carriage of malaria by mosquitoes 

 of the genus Anopheles, a number of observers in different parts of the world, 

 in addition to those already stated, had announced their belief in the relation 

 between mosquitoes and the malady. By far the most forcible argument, how- 

 ever, was presented by Dr. A. F. A. King, of Washington, in a paper read before 



