102 TRYPANOSOMES AND SLEEPING SICKNESS 



The fast-multiplying parasites do not remain in the blood of 

 their victim but penetrate many of the tissues and organs of 

 the body, especially the liver, spleen, lungs and lymph vessels 

 and glands. The last mentioned are probably one of the main 

 strongholds of the parasite in the body and the swelling of 

 lymph glands, especially in the neck, has already been men- 

 tioned as one of the characteristic symptoms of sleeping sickness. 

 The parasites are not present in constant numbers in the blood, 

 but periodically appear in large numbers and then apparently 

 disappear at fairly regular intervals. Often the trypanosomes 

 are so few in the blood that their presence can be proved only by 

 causing disease through the injection of some of the blood into a 

 susceptible animal or by causing the parasites to multiply, as 



they will quite readily do, in a 

 suitable artificial culture me- 

 dium. In Nigeria the parasites 

 are hardly ever seen in the blood 

 of infected persons, but they can 

 be found by puncturing a lymph 

 gland. According to recent 

 investigations by Fantham the 

 trypanosomes, probably as a re- 

 action against antibodies which 

 tend to destroy them, shrink into 

 FIG. 23. Agglutination of trypano- roun ded sporelike bodies with- 



somes, T. lewisi, in blood of immunized 



rat. (After Laveran and Mesnil.) Out locomotory organs but With 



a protective shell. In this 



condition they remain until conditions again become favorable 

 for them when they once more elongate, develop a flagellum and 

 undulating membrane, multiply and reappear in the circulating 

 blood. After several months or years the parasites penetrate 

 the cavity of the brain and spinal cord and live in the cerebro- 

 spinal fluid which fills it; this invasion of the central nervous 

 system is the direct cause of the dread sleeping sickness stage of 

 the disease. 



While under normal and favorable conditions the trypanosomes 

 merely live and multiply in the way described above, they are 

 capable of reacting in a very peculiar manner when exposed to 

 unfavorable conditions, such as the presence of drugs, low tem- 

 perature or administration of serum from an immune animal. 



