236 INFECTION AND IMMUNITY 



covered with a " green scum " and from which bub- 

 bles of gas are given off, have lost all terrors for the 

 well-informed man, except in so far as they serve as 

 breeding-places for mosquitoes of the genus Ano- 

 pheles. The green scum is made up of harmless 

 algae and the gas which is given off from the mud at 

 the bottom of such stagnant pools is for the most 

 part a well-known and comparatively harmless com- 

 pound of hydrogen and carbon methane or " marsh 

 gas." In short, we now know that the air in the 

 vicinity of marshes is not deleterious because of the 

 presence of any special kind of bad air in such local- 

 ities but because it contains mosquitoes infected with 

 the malarial parasite. 



The discoveries referred to, as is usual, have had 

 to withstand the criticism of conservative physicians, 

 who, having adopted the prevailing theories with 

 reference to the etiology of periodic fevers, were 

 naturally skeptical as to the reliability of the observa- 

 tions made by Laveran and those who claimed to 

 have confirmed his discovery. The first contention 

 was that the bodies described as present in the blood 

 were not parasites, but deformed blood corpuscles. 

 This objection was soon set at rest by the demon- 

 stration, repeatedly made, that the intra-corpuscular 

 forms underwent distinct amoeboid movements. No 

 one witnessing these movements could doubt that he 



