304 The Philippine Journal of Science mis 



A further attempt was made to solve the question of latent 

 infections by the experimental infection of animals, which could 

 be killed at different times after infection and in which the 

 behavior of the entamoebse in the intestine could be studied post 

 mortem. In these experiments 2 monkeys were fed repeatedly 

 with faeces containing encysted Ejitamoeba histolytica; 1 monkey 

 was fed a dysenteric stool; 1 monkey received, per oesophagus 

 after washing out the stomach with a suspension of magnesium 

 oxide, a bloody mucous stool by stomach tube ; 1 monkey received 

 an injection of dysenteric stool into the rectum ; 1 monkey received 

 an injection of dysenteric stool into the csecum; and 1 monkey 

 received an inoculation of entamoebic liver-abscess pus into the 

 liver. Two cats were fed encysted Entamoeba histolytica, and 

 6 kittens received rectal injections of dysenteric stools contain- 

 ing motile Entamoeba histolytica. One young pig was twice fed 

 large numbers of encysted entamoebse. All of the animals not 

 only did not develop dysentery, but in no case have they become 

 parasitized with Entamoeba histolytica. These results are sur- 

 prising in view of the experience of other authors who have 

 found animals, especially cats and monkeys, readily infected 

 with entamoebas by feeding or rectal injections of dysenteric 

 faeces. My results, while not numerous enough absolutely to 

 exclude the possibility of parasitizing animals with Entamoeba 

 histolytica, at least indicate that they are less readily parasitized 

 than men, 90 per cent of whom became parasitized in my 

 experiments. In consequence of these negative results from 

 attempts to infect animals with Entamoeba histolytica, no further 

 information was obtained in these experiments on the nature of 

 latency in entamoebic dysentery. 



Some light by analogy may be thrown on this subject by the 

 results of experimental infections of monkeys with Balantidium 

 coli which are now in progress. Balantidium coli produces a 

 serious and often fatal dysentery in man, but latent infections 

 which give rise to no clinical symptoms are as prevalent as in in- 

 fections with Entamoeba histolytica. In the experimental infec- 

 tions of monkeys, which almost invariably become parasitized 

 after feeding encysted Balantidium coli, there is the same latency 

 of clinical symptoms as in the human infections. One para- 

 sitized monkey killed one month after infection showed a slight 

 colitis with the balantidia penetrating the sound tissues of the 

 mucosa. Another monkey killed two months after infection 

 showed no colitis or ulcerations. And a third monkey, which 

 was dying five months after infection, was chloroformed, and 

 at necropsy the large intestine was found to have an extensive 



