190 DR. S. H. LONG ON THE MOSQUITO-MALARIA THEORY. 
in certain countries new-comers were almost certain to contract it. 
Not until the introduction of Peruvian Bark into Europe, in 
the seventeenth century, was any drug known which exercised 
a controlling influence upon the disease. In the year 1880 
a Frenchman named Laveran discovered with the aid of the 
microscope adventitious living organisms in the blood of those 
suffering from ague, and he rightly concluded that herein lay the 
cause of the disease. A good deal of scepticism was shown at first 
with regard to the identity of this parasite ; but thanks to the 
indefatigable labours of Dr. Manson and others, its causal relation- 
ship cannot now be denied by any one who is familiar with its 
life-history. 
It is necessary for me to say here that the parasite in question 
belongs to the Protozoa Class — Order Sporozoa. The characteristics 
of this order are that they consist of proper cellular elements, made 
up of protoplasm, a nucleus, and nucleolus. They possess Amoeboid 
movement, and are true Endo-cellular parasites, living at the expense 
of the cells they have invaded. They multiply by the formation of 
spores, hence their name. The Sporozoa are further divided into 
various Sub-orders, and it is to one of these — the Sub-order 
Haemosporidia — that the Ague parasite belongs. The main features 
of this Sub- order are an alternating generation with two evolutionary 
cycles ; the one endogenous and asporular, which determines the 
reproduction in the tissues ; the other exogenous and sporular, 
which permits contagion and ensures the conservation of the 
species. 
In the life-history of this Ague parasite, man forms the temporary 
host, and in his blood the asexual cycle is performed ; whereas 
the cycle of sexual life is completed in the Mosquito, which may 
therefore be called the definitive host. In the Mosquito the parasite 
reaches the salivary glands, and here they accumulate in large 
numbers. The Mosquito, biting man, inoculates him with its saliva, 
plus a certain number of the parasites, which, developing in the 
blood of man, produce those asexual parasitic generations which 
I have demonstrated to you under the microscope and by my 
diagrams. We thus see that in man the parasite lives in, and at 
the expense of, the red corpuscles of his blood upon which it feeds, 
and that concurrently with the different stages of an Ague attack 
it passes through a cycle of changes. It is now known, moreover, 
