520 FAMILY: TRYPANOSOMID^ 



exclude the possibility of infection after birtli from the milk or as a result 

 of mechanical transmission by insects. 



Trypanosomes as Filter Passers. — Various observers have tested the 

 capacity of trypanosomes to pass through porous filters which will 

 not allow the passage of bacteria. In the case of relapsing fever spiro- 

 cheetes it is known that the entire organism, probably on account of its 

 peculiar movements, is able to pass through such filters. In the case of 

 trypanosomes it is the opinion of some observers that this factor cannot 

 account for the passage through the pores of the filter, and that some 

 stage which is smaller than the usual form must exist. Novy and 

 MacNeal (1904a) first showed that the passage through a Berkefeld 

 filter of diluted blood containing T. lewisi yielded a filtrate which was 

 infective to rats. Experiments with T. hrucei gave negative results. 

 In these experiments, according to Wolbach, Chapman, and Stevens (1915), 

 the filters had been " thinned down " and were not shown to be impervious 

 to bacteria. Bruce and Bateman (1908) used filters which were proved 

 to prevent the passage of Micrococcus melitensis, and found that T. evansi 

 from the blood and organ juices of normal animals, and those which had 

 been treated with antimony and the cultural forms from blood-agar 

 medium, could not pass through. Bruce et al. (1911ji') again made 

 similar experiments with the developmental forms of T. gambiense in 

 Glossina palpalis, but obtained only negative results. Wolbach, Chapman, 

 and Stevens (1915) conducted a very careful series of experiments under 

 varying pressures in which care was taken to prevent the clogging of the 

 pores of the filters. Three trypanosomes were used- — T. gambiense, T. 

 brucei, and T. lewisi. The conclusion arrived at is that trypanosomes from 

 cultures and animal tissues are not filterable through bacteria-proof filters. 

 More recently Reich and Beckwith (1922) and Reich (1924) have repeated 

 the experiment. They used the macerated organs of guinea-pigs which 

 had died of T. brucei infections. The fluid was filtered after the addition 

 of a loopf ul of culture of Bacillus prodigiosus. The filtrate was immediately 

 inoculated into guinea-pigs, and a control culture was made on glucose 

 agar medium to determine the presence or absence of bacteria. In a series 

 of seventy-two experiments in which the filtrate was free from bacteria, 

 guinea-pigs became infected with T. brucei on twenty occasions. A series 

 of seven experiments made with highly infected blood taken from the 

 animals during life gave only negative results. It appears, therefore, that 

 the filterable form is to be found in greatest number in the organs, espe- 

 cially the liver and spleen, of animals which have died of an infection. It 

 does not follow from these experiments that invisible or ultra-microscopic 

 stages of trypanosomes exist. The plasticity of the body compared with 

 that of rigid bacteria would enable an organism to pass through narrow 



