233 FLAGELLATA. 



which belong to the family Monadinse. These creatures are, as their 

 name suggests, almost at the extreme limit of visible organisms ; they 

 are extremely small and transparent, and have generally very few, but 

 long, cilia (Figs. 117, 118), which sometimes propel the body rapidly 

 about, and sometimes merely vibrate to and fro. A slight amoeboid 

 movement is also occasionally to be observed. Almost all these Infu- 

 soria live on putrefying substances, and are often found in countless 

 numbers in water, or in living animals, especially in the rectum. 

 The species most familiar to us are those always present in myriads 

 in the large intestine of frogs and toads. In warm-blooded animals 

 the Monadinae are also among the most frequent of parasites. It is, 

 for instance, impossible to examine any ruminant or pig without find- 

 ing these creatures in countless numbers, along with other infusorial 

 parasites, in the paunch of the former, and in the ccecum of the latter. 1 

 In order to observe them, it is of course necessary that the examina- 

 tion should take place as soon as possible after death, since they soon 

 perish, and are then scarcely distinguishable from other small bodies. 

 Their occurrence in man, although not exactly rare, appears to be 

 always due to special circumstances, but when they occur it is usually 

 in great abundance. Their presence would also be much more fre- 

 quently ascertained if the evacuations could be immediately examined, 

 or even if it were possible always to use a warm stage. By this means 

 it is possible to keep the parasites alive for many hours, and to ob- 

 serve them in lively motion, if only care be taken that the preparation 

 does not dry up. 2 Slightly acidified water appears to be the best means 

 of moistening them, and is even capableof reviving theirflagging motion. 

 Temperatures above 50 C. and below 14 C. prove fatal, and thus the 

 fact is explained that parasites occurring in winter die in a few minutes, 

 especially if a cold glass slide be used. Further, as these creatures are 

 very sensitive to solution of corrosive sublimate, and perish imme- 

 diately when exposed to it, even when extremely dilute, this drug 

 would probably furnish a very efficient remedy for them. 



The parasitism of the Monadinse is, however, by no means confined 

 exclusively to the Vertebrata. In the genital canals of the snail, in 

 the body-cavity of the Kotifera, and in the alimentary canal of mille- 

 pedes and insects they are not at all uncommon, and occasionally are 



1 Gruby and Delafond have also observed Monadinse in the stomach of the dog 

 (Comptes rendus, t. xviL, p. 1304, 1843), and Davaine in the alimentary canal of the 

 guinea-pig, of the hen, and of the duck (loc. cit. ). [Grassi has recently described similar 

 forms in the guinea-pig, mouse, and duck (loc. cit.). R. L.] 



2 [Grassi (loc. cit.) refers the rapid death of the parasitic Monads, not so much to the 

 fall in temperature, as to the rapid formation of acids in the evacuated faeces. Where this 

 is prevented, the Monads may remain alive for many days. R. L.] 



