EXPERHIENTS ON BIRD MALARIA 387 



stopping the bleeding after the needle is withdrawn, not only to 

 prevent the loss of too much blood but to avoid thrombosis. If 

 the vein is pressed too tightly or too long, or if its wall has been 

 much injured thrombosis is quite certain to occur. Aseptic pre- 

 cautions are not particularly necessary in work of this sort with 

 birds, for they are very resistant to bacterial infection, nor do they 

 seem to sufifer much pain during the process. It is good practice 

 to first clean all the areas with seventy per cent alcohol, however. 



12. Number of parasites necessary for infection. The number 

 of parasites required to infect a fresh canary varies with the 

 weight of the bird, and with its natural resistance. Boyd (1925) 

 found that if fewer than 1,000 parasites were injected infection 

 seldom resulted, but more than this number were usually effective. 

 When more than 10,000 were used inoculations were nearly always 

 successful. In practice it is usually sufficient to take fifty cubic 

 millimeters of blood from an active case, and less than this amount 

 is often enough. 



If for any reason a fresh bird cannot be immediately inoculated 

 no harm will be done if the infective mixture is allowed to stand 

 for several hours ; the parasites appear to be very resistant to 

 cooling and such a mixture has been found infective even after 

 twelve hours. If placed on ice they remain alive much longer 

 than this. 



13. Cultivation. Although the parasites of human malaria have 

 been successfully cultivated by Bass and others, those of bird 

 malaria have not as yet been cultured outside the body of the 

 host, although the same technique has been employed as for the 

 parasites of man. It is likely that the chief reasons for lack of 

 success lie in the necessarily small amounts of blood used. When- 

 ever a simple and practical method of cultivating the avian para- 

 sites is devised the way will be opened for many experiments of 

 the most fundamental importance. 



14. In znvo preparations. ]\Ialarial parasites may be studied 

 either in vivo or in vitro. If the living parasites are to be studied 

 it is only necessary to mix a very small amount of blood from a 

 well-infected bird with a drop of physiological saline, or citrated 

 salt solution of similar tonicity, mount under a coverglass and 

 observe with the microscope. Exflagellation can be very prettily 

 observed under such circumstances, if gametocytes are abundant 

 (the number of gametocytes reaches a maximum about one day 



