MODIFICATION OF BIRD MALARIA INFECTIONS 409 



tive organism and little influenced by conditions which may sur- 

 round the host or the parasite. 



Protozoa in general do not seem to follow such regularity in 

 the matter of reproduction and this fact leads one to question 

 the above-mentioned assumptions in regard to the cause of period- 

 icity in malaria. ^Accordingly, experiments were undertaken by 

 the writer (see Boyd, 1929a and 1929&) to determine whether 

 the reproductive activity of these parasites is definitely fixed or can 

 be modified by alterations of the environmental influences which 

 usually surround these infections. These experiments may be 

 grouped under the following heads : 



1. Reversal of the daily cycle of activity and rest for infected 

 birds. 



2. Simultaneous inoculation mith two groups of parasites dif- 

 fering in their periodicity — that is, so-called double infec- 

 tions. 



3. Variation in length of the experimental day and night for 

 infected birds. 



4. Continued exposure of infected birds to an experimental 

 day and night of fourteen hours each. 



Material and general methods of procedure. The parasites used 

 were from a strain obtained by Dr. Ernest Hartman from an 

 English sparrow in Baltimore, Maryland, in 1924, and later de- 

 scribed by him under the name of Plasmodium cathemerium. 

 Female canaries were used as the experimental host in these 

 studies. The infection was transmitted to these canaries by direct 

 inoculation with a small number of parasites from a previously 

 infected bird. In the efifort to control experimentally the cycle 

 of daily changes which normally go on in infected birds and 

 their parasites an attempt was made to simulate day and night 

 in an artificial way by shifting these infected birds alternately 

 at chosen intervals between a room which was lighted by means 

 of an arc lamp giving approximately 3000 candle power illumina- 

 tion and a dark, unheated closet. 



In order to follow the reproductive activity of the parasites 

 under the experimental conditions, blood smears were taken from 

 the infected birds at intervals of two hours throughout the period 

 of study. These smears were stained with MacNeal's tetrachrome 

 stain. The tetrachrome stain was used in preference to others 



