PATHOGENIC PROTOZOA. 409 



observed. Conjugation has also not been observed at least 

 satisfactorily. The blepharoplast is the first to begin dividing, 

 the flagellum remaining attached to one of the resulting halves, 

 while a new flagellum develops on the other half. The division 

 of the nucleus follows next in order as a rule, though this may 

 precede the division of the blepharoplast. The active division 

 of the nuclei and plepharoplast give rise to rosette formation 

 owing to delayed division of the cell protoplasm. 



Cultivation of Trypanosomes. — Many trypanosomes are 

 much alike morphologically so that they are hardly dis- 

 tinguishable with the microscope alone, but in cultures the 

 different species present points of difference. The culture 

 medium adapted to their growth consists of equal parts of 

 defibrinated rabbit's blood serum and ordinary nutrient 

 agar. The method of preparation of the medium consists 

 in melting up tubes of agar and after cooling them down to 

 50° C. adding the blood-serum. The tubes are allowed to 

 set in an inclined position, then stood upright to allowed the 

 water which separates out to accumulate at the bottom of the 

 incline. Tubes should be fresh, since it is necessary to have 

 abundant moisture in the tube. After inoculation, the tubes 

 are kept at 25° C. or in the room. First growth is observed 

 in about three or four days to one week. Initial cultures are not 

 so vigorous as subsequent cultures. Usually there is no 

 growth visible with the naked eye, but sometimes the growth 

 is evdent in this way. Pure growths may be obtained by 

 making streaks on blood-agar plates. The forms met with 

 in cultures differ from those seen in the blood of an infected 

 animal. They are usually smaller- in the cultures than in 

 the blood, although sometimes they are much longer than 

 these. The blepharoplast is usually, though not always, 

 lateral or anterior to the nucleus in the cultivated forms. 

 Some species, as Tr. avium, show two distinct forms in cultures 

 giving rise to the suggestion of sexual difference. Trypano- 



