Insects and Disease 6 1 9 



in the blood -iDrpusclcs, using up tlicir substance and breaking them down, 

 must work much iiarm to the human body. This harm is exactly that which 

 we recognize as the result of malaria. The fever and other ills that are a 

 part of malaria are the direct and indirect pathological effects of the growth 

 and metabolism and multiplication of the Hsemamcebae in our blood. From 

 a single infection the sporulation or escape of the myriads of spores from the 

 breaking-down corpuscles into the blood-plasma takes place practically simul- 

 taneously and makes the beginning of the malarial spasm. This kind of 

 multiplication of the H;cmama'bx% by sporulation, is termed ase.xual; there 

 is no participation of individuals of two kinds, or sexes, in the reproduction. 

 It is a sort of multiplication common to a great many minute, simple animals 

 and plants, but it does not seem in any of these to be the only mode of mul- 

 tiplication. Scores, even hundreds, of successive generations may be pro- 

 duced asexually, but finally there occurs another kind of reproduction, which 

 has for its essential characteristic the meeting and fusing of the nuclei or 

 parts of them, and sometimes the body protoplasm or parts of it, of two 

 individuals of the species. In all but the very simplest organisms these two 

 conjugating individuals differ somewhat in size, shape, and manner of behavior. 

 Scientists began to ask when and how and where conjugation occurred in 

 the Ha'mamoL'ba; of malaria; their questioning was made more insistent by 

 the discovery that some of the amoebulae in the blood -corpuscles did not sporu- 

 late, but continued to circulate in the blood without any particular function 

 at all. More than that, it was noted that whenever they were withdrawn 

 from the circulation, as when a drop of blood was taken out of the skin with 

 a pipette for exainination under the microscope, these traveling amoebula; 

 would swell up and liberate themselves from their enclosing corpuscle, and 

 that some of them would emit a number of long motile filaments; these fila- 

 ments could be seen lashing about strongly, and often succeeded in breaking 

 away from the i)arcnt cell, and darting away among the corpuscles. This 

 phenomenon can always be observed in the blood drawn from a malarial 

 patient, in from ten to fifteen minutes after its withdrawal from the circula- 

 tion. What is the meaning of it ? A further insistent question came up at 

 this time. And that is, If the Hsmamceba; are the actual and sole cause of 

 malaria, how do they get from man to man? How is the malaria dissem- 

 inated ? 



The explanation of the signiticancc of the phenomenon of the formation 

 of the motile filaments from amoebulae in blood withdrawn from circulation, 

 and the answer to the question as to the mode of transmissibility of malaria, 

 are closely connected, and were reached chiefly through the brilliant work 

 of Manson and Ross, two English investigators of tropical di.sea.ses. Espe- 

 cially interesting is the work of Ross in establishing the actual fact of the carry- 

 ing by the mosquito of the Hiemamockc from man to man. The following 



