136 CnEMISTBY OF THE AXIMAL PARASITES 



observers have suggestecl the possil)ility of obtaining artificial im- 

 munity against protozoa, and Rossle ^- has obtained immune sera 

 against infusoria. 



The serum of rabbits immunized against amoebae was found by 

 Sellards ^^ to be cytolytic for the same amoebae, but no antibodies 

 could be found in the blood of patients with amebic dysentery. 

 Novy ^* has obtained immunity against trypanosomes, but the serum 

 of immune animals will not confer passive immunity. Braun and 

 Teichmann,^^ however, claim positive results with immune serum 

 from rabbits; they found no poisonous agent in trypanosome sub- 

 stance.^^" The fact that trypanosomes themselves readily become im- 

 mune to various trypanocidal chemicals has been demonstrated and 

 extensively studied in Ehrlich's laboratory. Gonder ^"^ has made the 

 niteresting observation that trypanosomes which can be stained by 

 certain vital stains, become unstainable while alive if immune to 

 arsenic compounds, suggesting that this immunity is associated with 

 considerable structural or chemical changes. 



Plasmodium malarise undoubtedly produces toxic substances, which 

 seem to be of such a nature that they do not diffuse from the red 

 corpuscle, but are only liberated when the corpuscle breaks up on 

 the maturation of the parasite. In this way the characteristic par- 

 oxysmal manifestations of the disease are produced. The nature of 

 the poison or poisons is unknown, but we have evidence that it is 

 hemolytic, since malarial serum may hemolyze normal corpuscles,^" 

 and extracts of the parasites are strongly hemolytic (Brem^®) ; prob- 

 ably the malarial hemoglobinuria is caused by this hemolysis. Pre- 

 sumably malarial poisons are not extremely toxic for parenchymatous 

 cells, since the parenchymatous lesions in malaria seem to be relatively 

 slight as compared with the intensity and duration of the intoxication. 

 Some authors state that the toxicity of the urine is increased after 

 the paroxysm,^** which, however, does not necessarily indicate that 

 a poison formed by the parasites is excreted in the urine. Immunity 

 seems to be seldom developed against the malarial poison or against 

 the parasite itself, although some persons seem to be naturally im- 



12 Arch. f. Hvfj., 1905 (54), 1; full review of this topic. 



13 Philippine" Jour. Sci., 1911 (6). 281. 



14 Jour. Infec. Dis., 1912 (11). 411. 



isZcit. Immunitiit., Ref., 1912 (6), 4G5. • 



isallintze (Zeit. f. Hyp:., 1915 (80), .377) obtained little immunity with T. 

 hrucei. hut Schillinfj and Rondoni (Zeit. Immunitiit., 1913 (18), 651) obtained a 

 yxiison from Napana trypanosomes which produced active immunity in mice. 

 When trypanosomes are killed by weak electric currents they may liberate an 

 active poison (Uhlenhuth and Sevderhelm, Zeit. Tmiminitiit., 1914 (21), 30()). 



10 Zeit. Immunitiit., 1913 (15)," 257. 



17 See Repnault, Revue de IVIed.. 1903 (23), 729. 



18 Arch. Int. Med., 1912 (9), 129. 



19 Quoted from Blanchard, Arch. d. Parasitol., 1905 (10), 83; this article pives 

 a resume of the subject of the toxic substances produced by the animal parasites. 



