THE PATHOGENIC PROTOZOA 145 



they conceal their origins, of which we can with difficulty 

 discover a few vestiges. 



The protozoa may injure their host both by mechanical 

 and by chemical means. The Entamoeba histolytica destroys 

 and strips the epithelial cells from the intestine, abolishing 

 at certain points the impermeability of the healthy mucosa. 

 Myxobolus pfeifferi produces atrophy of the muscle fibres. 

 Lentospora destroys the bones and cartilages of the trout. 



The, toxins of the protozoa are little known. If they exist 

 they are difficult to isolate and demonstrate. The Sarcocystine 

 of Laveran and Mesnil, which kills the rabbit and only the 

 rabbit, is a well-characterised toxin, but no similar substance 

 has been isolated from the cultures of trypanosomes, or from 

 the blood of animals with a trypanosome infection. The blood 

 of a malarial patient, filtered at the moment of the paroxysm, is 

 not quite harmless to a healthy individual. The blood of an 

 animal infected with trypanosoma gambiense produces an 

 appearance of somnolence in experimental animals, but it is 

 difficult to say how much of this is due to products of the 

 parasite and how much to the host. These are researches 

 which will have to be continued ; there is no reason to believe 

 in- advance that toxins and endotoxins do not exist in the 

 pathogenic protozoa. 



Heredity in Protozoal Diseases. — The protozoa are 

 frequently intracellular parasites. Bacteria also may inhabit 

 cells, for example the bacillus of leprosy, the bacillus of swine- 

 erysipelas, and the tubercle bacillus. . But in these cases it is 

 the cell which has taken up the bacterium, the cell being 

 mesodermic and naturally phagocytic ; the microbe has been 

 captured ; no bacterium ever penetrates by its own activity 

 into a living cell. On the contrary, many protozoa have during 

 their life-cycle a motile form, amoeboid or flagellate, thanks to 

 which they can penetrate spontaneously the cells of their 

 host. 



This fact is of capital importance from the point of view of 

 heredity in disease. When one sees the young of an anthrax- 

 infected mother born with an anthrax pustule, one might think 



