205 
LIMITS OF INFECTIOUSNESS OF MAN 
During the progress of the experiments it was noticed that 
patients were discharged after their temperature had become normal 
and when their peripheral blood occasionally contained more than 
a sufficient number of gametes to infect susceptible mosquitos. In 
order that a recommendation might be made for the continued 
treatment of these persons, it was necessary to determine, if possible, 
the limits of infectiousness of such individuals. 
Several experiments were carried out, in which Ce. albimana 
bit patients whose gametes per leucocytes had been determined. 
These mosquitos were given but one blood feeding and fed 
subsequently on dates and raisins and then dissected. I he limits 
were determined as being near one gamete per 500 leucocytes, or 
twelve gametes per mm. 3 ; but it must be understood that several 
factors are concerned in infections, such as number and phagocytic 
power of leucocytes ; immunity of mosquitos, racial and individual; 
probable reaction of gut contents, as acid bacterial products or 
those from yeasts, may be inimical to the gametes; and again 
proportion of 9 to £ gametes plays some part, besides the number 
of gametes ingested. In Experiments 20 and 28 patients blood was 
rich in crescents which flagellated in vitro, and in the mosquitos 
stomach, yet mosquitos never could be infected from the patients. 
Persons with more than twelve gametes per mm. 3 must be 
regarded as gamete carriers, and, of course, should not be 
discharged from hospital nor should treatment be discontinued 
until gametes have been reduced well below the limits of infectious¬ 
ness. This destruction and prevention of the development of the 
sexual forms of the parasite in man is a matter generally over¬ 
looked, but is of the greatest importance in delimiting malaria, 
and it may be accomplished by appropriate quinine treatment of all 
gamete carriers ; by quinine treatment to destroy latent malaria, and 
by periodical blood examination of labourers and others in quarters 
where there is a high malarial rate. For the detection of gamete 
carriers and latent malaria, in order to carry out appropriate treat¬ 
ment, 30 grains of quinine sulphate in solution daily is an efficient 
dosage for the purpose required. 
