ESSAYS ON BACTERIOLOGY. 41 



severity of a single case or tlie character of an epi- 

 demic,) will find their explanations in this hypothesis. 



Reference ought here to be made to at least one 

 other disease, namely, malaria. It is well known that 

 there has been, fonnd a peculiar body in the blood of 

 those suffering from this malady, called after its dis- 

 coverer the Plasmodium of Laveran. It is described 

 as a low organism, not belonging to the class of bac- 

 teria, but to the animal kingdom, to be included 

 among the protozoa or mycetozoa, and for this reason 

 named plasmodium. It is found within the red cor- 

 puscles. The organism is small, round or irregular, 

 having a rapid amasboid movement; it grows rapidly, 

 soon fills the larger part of the corpuscle, and before 

 long is found to contain many roundish granules or 

 rods consisting of black pigment. It is easily recog- 

 nized, stained or unstained, in the blood freshly taken 

 from the finger during the attack. It has never been 

 artificially cultivated. Inoculation experiments are 

 therefore wanting. But by agreement among many 

 investigators in Europe and America, it is of great 

 value in diagnosis, enabling us to distinguish with cer- 

 tainty between malaria and other fevers. This fact 

 at once makes it of much practical interest. 



Another important matter is now 'arising in the field 

 of bacteriology. The germ theory of disease is set- 

 tled; it has become an established fact. But what 

 does it mean and whither is it leading us? Why these 



