78 THE AMERICAN MONTHLY [Mar 
were of crescentric shape. These species received the ti- 
tle astivo-autumnal, on account of the season in which it 
showed itself in Italy. It was not so regular in its pe- 
riods as the others, and was much more dangerous. The 
existence of these different species was at first very gen- 
erally doubted, but it is now universally accepted,and is 
of very great importance. The examination of a drop of 
‘blood from the finger of the patient enables the physician 
to decide not only whether the disease is malaria, but 
which of the three types it will follow. The more dan- 
gerous crescent form is commonest in the Tropics, and 
hence has been termed by Koch tropical malaria. The 
quartian has proved the mildest of the three. The pro- 
cess of sporulation might seem at first sight to explain 
the whole life-history of the parasites. For their propa- 
gation within the human body that process does indeed 
make ample provision. But the mystery remained—how 
did they gain entrance into the human system? Though 
present in abundance in the blood of the malarial patient, 
they are absent from the excreta. Spontaneous genera- 
tion having been long since exploded, what could be their 
mode of origin in the external world? This problem has 
of late been completely solved. Among the forms of the 
parasite observed by Laveran was one which he termed 
‘flagellated,” possessing filamentous appendages which 
exhibit extremely active movements, by virtue of which 
they were often seen to break off from the parent microbe 
and swim away. These flagella were regarded by many 
biologists as products of degeneration resulting from the 
abnormal influences to which the parasites were exposed 
in blood outside the body. This Laveran could not be- 
lieve ; indeed, it was the remarkable activity of the flag- 
ella that finally satisfied his own mind that what he had 
discovered were really living parasites ; he regarded the 
flagella as the highest form of development of the mi- 
crobe. There was another observer who felt equally con- 
