182 MICROBES, FERMENTS, AND MOULDS, 
while their seven ‘children, who slept on the second 
floor, escaped. Salisbury ascertained that there was 
a fog every morning, rising from a reservoir which 
had been recently made. This fog reached the house 
and rose above the first floor, but not as high as the 
windows of the second floor, and penetrated into the 
parents’ bed-chamber through the open window. This 
vapour had the same smell as the marsh, which was 
covered with fever algze (Palmella febrilis), and pro- 
duced the same feverish dryness in the throat and 
pharynx. The vapour dispersed soon after sunrise, 
and before the children had left their chamber. 
Salisbury likewise ascertained the polymorphism 
of Palmella febrilis, a polymorphism which is con- 
firmed by the recent observations of the skilful 
naturalist Zopf, and this fact explains the mode in 
which an aquatic alga can live in the human blood, 
in the form of Bacillus or Spirillum. 
Still more recently (1879), marsh fever, or malaria, 
which is so common in Sicily and in the Roman 
Campagna, have been studied from the same point 
of view by Crudeli, Cuboni, Cecci, and others, who 
ascribe the disease to a vegetable parasite which they 
call Bacillus malariw. This bacillus is abundantly 
found in the blood of patients during the period of 
attack, while during the period of acme which ter- 
minates each attack only spores are found. The same 
microscopic organism is found in all the malarious 
districts of the Roman Campagna, and it can be 
