640 POPULAR SCIENCE MONTHLY, 



tions of India, is believed to be due to a similar parasitic protozoan 

 (Trypanosma Evansi). According to Lingard, this infusorium 

 exists as an innocuous parasite in the blood of rats in India. It 

 is not pathogenic, or only feebly so, for the native ox of India, 

 but gives rise to a fatal infectious disease in horses, dogs, and 

 camels. 



Another pathogenic micro-organism belonging to the protozoa 

 is the Amoeba coli, which is found in great numbers in the large 

 intestine in cases of tropical dysentery and also in liver abscess 

 secondary to this disease. 



The rapid progress of our knowledge of the bacteria has been 

 due to the fact that satisfactory methods (staining) have been 

 devised for detecting these minute micro-organisms in the blood 

 and tissues of infected individuals and for cultivating them in 

 artificial media. Unfortunately, these methods have only a limited 

 utility when applied to investigations relating to the protozoa. 

 The bacterial cell has considerable stability, owing to its cellulose 

 envelope (cell wall), and it is readily stained by the aniline dyes. 

 The protozoa, on the contrary, very readily undergo disintegra- 

 tion, and the more fluid protoplasm of these unicellular organisms 

 is not so easy to demonstrate by the usual staining reagents. It 

 has also been found very difficult, and in many cases quite impos- 

 sible, to obtain pure cultures in artificial media. Again, the recog- 

 nition of protozoa in the blood of infected animals by means of 

 the microscope requires special skill in making preparations, in 

 the management of the light, etc., and expert knowledge of the 

 normal elements of the blood and of the changes they undergo as 

 a result of various methods of preparation. This is illustrated 

 by the fact that many persons, more or less familiar with the use 

 of the microscope, have failed to discover the malarial parasite in 

 blood which undoubtedly contained it, while others have evi- 

 dently mistaken vacuoles in normal blood- corpuscles for the Plas- 

 modium, the crenated red corpuscles for pigmented cells, and 

 deformed corpuscles for malarial crescents. 



Notwithstanding the painstaking researches which have been 

 made during the past few years for the purpose of determining 

 the nature of certain bodies which may be demonstrated by spe- 

 cial staining methods in the cells of carcinomatous tumors, we are 

 still uncertain as to the nature and ^etiological import of these 

 bodies. Some investigators believe them to be protozoa, and from 

 their location infer that they are the specific ^etiological agents in 

 the development of malignant growths of this character. But, so 

 far as we are informed, this view has not as yet received any 

 very substantial support, and has not been accepted by the lead- 

 ing pathologists of the world. 



The presence of amoeboid micro-organisms in the contents of 



