MEDICAL ENTOMOLOGY HOWARD. 569 



by dipping county after county has been retrieved from quarantine 

 and now a vast area, formerly dangerous, is fever free. Curiously 

 enough the old fever quarantine line corresponded closely to the 

 dividing line between the upper and lower austral life zones on 

 Merriam's early life-zone maps of the United States. Theoretically, 

 therefore, the cattle tick is a lower austral form and can more easily 

 be exterminated from its more northward range. But cattle culture 

 can now be carried on with profit in many regions of the South 

 where diversified agriculture has become a necessity. 



This in itself is a noteworthy result of Smith's discovery, but 

 biologically it is of the very greatest importance as the pioneer dis- 

 covery of a blood-inhabiting protozoan in its dual relation between 

 an articulate and a mammalian host. It is true that the cattle tick 

 is not, strictly speaking, an insect, but it is closely related to the 

 insects and is popularly called one, so that this demonstration, first 

 described in full in 1893, ranks as the second great discovery in 

 medical entomology. 



While Smith was completing his college course at Cornell, Dr. 

 A. Laveran, a French Army surgeon, was studying malaria in Algeria 

 and succeeded in 1880 in demonstrating an ameboid organism in the 

 blood of malarial patients, which he studied at length and showed 

 to be the causative organism of the disease, which thus became estab- 

 lished as a parasitic malady. The details of the life cycle of this 

 organism as it occurs in man were traced by Laveran after the dis- 

 covery of the true cause of the disease, and there was much specu- 

 lation as to the manner in which it is transferred to healthy people. 

 The drinking of contaminated water was an early suggestion and 

 there were others, but experimental work failed to prove their truth. 

 Laveran himself eventually suggested that the parasitic organism 

 might be carried by mosquitoes, but Manson, after his success with 

 Filaria, insisted upon the necessity for experimentation with these 

 insects and formulated the hypothesis that they might be the neces- 

 sary secondary hosts. It was, in fact, largely due to Manson's sug- 

 gestions that Ronald Ross, then a surgeon in the Indian Medical 

 Service, began his studies. 



The details of Ross's work have now become well known among the 

 medical profession and those engaged in sanitary work. Starting 

 with nothing but a theory and a knowledge of the appearance of the 

 parasite after it appears in the blood of man, but with no knowledge 

 whatever of how it might look in another stage of its development 

 or whether it might be found in one kind of mosquito and not in 

 another kind, Ross spent two years and a half of the most strenuous 

 work before he solved the question and found the parasites among 

 the cells of the stomach of what he termed " dapple-winged mos- 

 quitoes." This result was reached in August, 1897, and after its 



