BIOLOGICAL SCIENCE 63 



In many cases the action of the microbe on the 

 body it attacks is directly due, not to the microbe 

 itself, but to a chemical substance, or enzyme, it pro- 

 duces. In 1897 this process was first demonstrated 

 by Biichner for the fermentation of yeast : its charac- 

 teristic effects could be induced by a substance 

 extracted from the cells. These enzymes seem them- 

 selves to remain unchanged at the end of the action, 

 their presence alone being sufficient to work the 

 changes. 



The history of the discovery of the true nature 

 of malarial fever may be taken as a typical example 

 of the romance of modern biology. The forging of 

 the first link in the chain was due to Laveran, a 

 French army doctor, who, in 1880, detected living 

 parasites in the blood of a malarial patient. The 

 clue was followed up in Italy, where the life history 

 of these microbes was studied. Three distinct groups 

 were distinguished at first, corresponding to three 

 different forms of the disease prevalent at different 

 periods of the year. The interest now centred in 

 finding the means by which the infection was intro- 

 duced into the body of man ; naturally, some suctorial 

 insect was soon suspected. In 1895, Ross and Manson 

 were able to demonstrate the existence of the identical 

 parasites in mosquitoes which had fed on the blood 

 of infected persons, and showed how the parasites 

 increased in size, divided, and became full of thread- 

 like spores until their progeny filled the body cavity 



