PROTOZOA 131 



dysentery. There is also no evidence, clinical or experimental, 

 that amebic infection causes the formation of anti-substances of 

 any kind in the body of the host. The spontaneous recovery 

 from amebic and other protozoan infections, however, may be 

 considered as indicating the development of an immunity 

 against these organisms. Numerous observers have suggested 

 the possibility of obtaining artificial immunity against protozoa, 

 and Rossle l has obtained immune sera against infusoria. 



Plasmodium malarias undoubtedly produces toxic sub- 

 stances, 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 paroxysmal 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. 2 Presumably it is not ex- 

 tremely toxic for parenchymatous cells, since the parenchyma- 

 tous 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, 3 which, however, does not necessarily indicate that a 

 poison formed by the parasites is excreted in the urine. Immu- 

 nity seems to be seldom developed against the malarial poison 

 or against the parasite itself, although some persons seem to be 

 naturally immune, while some acquire immunity through previ- 

 ous infection. 4 Many writers have looked upon the pigment 

 present in the malarial parasites as a true melanin, produced by 

 their metabolism and not a product of decomposition of hemo- 

 globin; however, Ewing 5 found that it showed the same relation 

 to solvents as the blood-pigments (See " Pigmentation," Chapter 

 xvi). 



Sarcosporidia of sheep (Balbiania gigantea, Railliet) 

 yield aqueous and glycerin extracts that are highly toxic for 

 rabbits (Pfeiffer), the poisonous constituent of which was called 

 sarcocystin by Laveran and Mesnil. 6 This is so highly toxic 

 that 0.0001 gm. is fatal to rabbits (per kilo), other animals 

 being less susceptible. It loses its toxicity on heating at 85 



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



2 See Kegnault, Revue de MeU, 1903 (23), 729. 



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

 gives a resume of the subject of the toxic substances produced by the animal 

 parasites. 



4 See Celli, Cent. f. Bakt., 1900 (27), 107. 



5 Jour. Exper. Med., 1902 (6), 119. 

 6 Compt. Kend. Soc. Biol., 1899 (51), 311. 



