OBSERVATION AND EXPERIMENT 83 



7. Their local prevalence in the autumn is always checked by 

 a decided frost." 



Here we have the facts with regard to the symptoms and 

 cause of the disease stated with a clearness and a conciseness 

 that could hardly be surpassed. But the real cause of the 

 malady eluded the insight of the discriminating observers who 

 collected those facts. A quite different class of facts required 

 consideration. It was essential to concentrate attention on the 

 pathological aspects of the enquiry. As to the nature of the 

 disease Hartshorne writes, with commendable caution, " It is 

 only possible to speculate at present. It is most probable that 

 ague is a toxemic neurosis. The importance of the blood 

 change attending it is shown by the disintegration of the blood 

 corpuscles, and deposit of pigment in various organs." This 

 destruction of the blood corpuscles was the critical point on 

 which the investigation turned. About 1 880, Laveran, a French 

 army surgeon, discovered the destructive agency in a minute 

 parasite, one of the protozoa, which takes up its residence in, 

 and then ungratefully enough, destroys our red blood corpus- 

 cles. What a splendid problem was presented by the facts thus 

 brought to light! The exquisite refinement of the researches 

 which followed may be inferred when we reflect on the minute- 

 ness of an organism which can work out a part of its life his- 

 tory within blood corpuscles so small that four to six millions 

 of them find plenty of room in a cubic millimeter. But 

 stranger still is the fact established within the past year or two 

 that the mosquito plays the role of an intermediary host and 

 transmits the parasites to us while feasting upon our blood. 

 The details of this remarkable discovery need only be alluded 

 to here, for they have been so recently explained by the experts 

 participating in them that their essential features are a part of 

 popular information. Suffice it to remark that they show how 

 we may secure almost complete immunity from malarial fev^ers 

 at no distant day. 



Thus, in whatever direction we look for the sources of scien- 

 tific progress, the same elementary' methods of advancement 

 are found to be effective. Whether we consider the dimensions 



