CHAPTEE LIT. 



TRYPANOSOMES AND TRYPANOSOMIASES CERCOMONAS 

 TRICHOMONAS HERPETOMONAS. 



TRYPANOSOMES. 



Historical. Trypanosomes were first seen by Valentine in 1841 

 in the blood of trout, and in the following two years they were found 

 by several observers in the blood of a number of species of frogs. 

 The first trypanosomes in a mammal was discovered by Lewis in 

 India, in 1878, in the blood of the rat. Two years later Evans, chief 

 veterinarian of the English Army in India, discovered trypanosomes 

 in the blood of horses, camels, and other animals sick with the affection 

 known as surra, and he expressed the opinion that these blood para- 

 sites were the cause of the disease. This claim was, however, at 

 that time not widely accepted and the study of trypanosomes as an 

 etiologic factor of disease was not extensively undertaken until Bruce, 

 in 1894, had discovered trypanosomes as the cause of nagana of 

 horses and cattle in Africa. Since that time these flagellata have 

 been discovered in a number of animal diseases, and today their great 

 importance in veterinary and human pathology is well established. 



Classification and Morphology. Trypanosomes belong to the proto- 

 zoan subphylum mastigophora (whip carriers), to the first class 

 (zoomastigophora) in which animal characteristics are predominant, 

 and they form the fourth order of this class. They are defined by 

 Calkins as follows: "Organisms of elongated, usually pointed form, 

 and a parasitic mode of life, with one or two flagella arising from 

 a special motor nucleus, and with an undulating membrane provided 

 with myonemes running from the kinetonucleus to the extremity of 

 the cell; one of the flagella is attached to the edge of this membrane 

 throughout its length, and may terminate with the membrane or 

 be continued beyond the body as a free lash." 



Trypanosomes generally have an elongated spindle-, lancet-, or 

 eel-shaped protoplasmic body; sometimes the spindle is almost as 

 wide as it is long. This, however, is only exceptionally the case, and 

 the student first familiarizing himself with trypanosomes, particularly 

 those in higher vertebrates, will do well to remember them as little, 

 rather slender, eel-shaped bodies of the size of an involuntary muscle 

 cell of the non-pregnant mammalian uterus. Their protoplasm shows 

 two chromatic or nuclear masses. One of them, as a rule, placed at or 

 near the centre is a comparatively large, finely granular body, called 



