DR. S. H. LONG ON THE MOSQUITO-MALARIA THEORY. 191 
that a different parasite is associated with the different kinds of 
Ague — tertian, quartan,* &c., so that by examining the blood of 
a suspected case and finding the parasite, the kind of Ague from 
which it has been taken can be identified. This can be done by 
merely taking a drop of blood from the finger and examining it 
under a high power of the microscope. This cycle of change in 
the blood of man had been accurately noted by several independent 
observers ; but the question to be settled was, how did it gain entry 
into the blood, and what was the animal or insect in which the 
other part of its life-history, i.e., the sexual cycle of its existence, 
was passed 1 
In 1894, Manson originated the idea that the malarial parasite 
was capable of an existence outside the human body, in which the 
“ flagellate ” form played an important role ; and he was led to 
suggest that the Mosquito served as the definitive host for the 
further development of the parasite, as it was known to do for the 
Filaria nocturna, which is the cause of certain other tropical 
diseases, and which has I believe on a previous occasion been 
demonstrated to this Society. 
At the instigation of Dr. Manson, Surgeon-Major Ross of the 
Indian Medical Service went out to India to make experiments and 
investigations on this point. A laboratory in Calcutta was set 
apart for his use, and in February, 1898, Ross commenced his 
investigations. There being few cases of human Malaria at this 
season of the year, Ross turned his attention to certain birds, such 
as Sparrows, containing in their blood the form of bird parasite 
known as Proteosoma grassii. He made a certain kind of Mosquito 
( Culex pipiens ) bite infected birds, and by successively dissecting 
each day a Mosquito of those which had bitten the birds he dis- 
covered the life cycle cf the Haemosporidia in this insect. He 
discovered that the pigmented bodies grew rapidly within the 
Mosquito till in about a week they projected like buttons from the 
outer surface of the stomach. Having reached maturity they burst 
into the general body cavity, setting free enormous numbers of 
so-called “germinal rods.” These latter were found soon to leave 
the body cavity and to accumulate in the cells of the salivary or 
poison glands, and in the duct leading from them to the proboscis, 
* The differentiation between the tertian and quartan forms of fever was 
first demonstrated by Golgi, of Pavia, in 1889. 
