ENTOZOA IN THE AREOLAR TISSUE. 209 



the tissues, and continue their development in that 

 situation. Dr. Davaine observes that this may be 

 answered negatively for two reasons ; the first, that 

 the rupture of a filaria whilst situated within the 

 human body is not followed by a new generation of 

 filarise ; and the second, that the Guinea-worm is not 

 propagated in countries which are situated much to 

 the north of the tropics, although the larvae may be 

 kept alive for several days by placing them in water. 

 According to these facts, it may be considered pro- 

 bable that the embryo must acquire a certain degree 

 of development externally to the human body before 

 its introduction into it, so as to attain the adult state, 

 and also that the tropical heat is requisite for the 

 accompHshment of that part of its development 

 which takes place before it finds its way into the 

 body. 



It is generally acknowledged by the writers who 

 have had ample opportunities for the observation of 

 the attacks of the Guinea-worm, that its appearance 

 and relative frequency are in some manner connected 

 with the heavy periodical rains, with the degree of 

 humidity of the locality, and with the extent and 

 position of the marshes and rivers ; but these authors 

 do not agree as to the mode in which the filaria 

 enters the human tissues. 



Some have strongly upheld the opinion that the 

 larvae of the filaria are taken into the stomach with 

 the water which is employed for drinking purposes, 

 and that they then penetrate amongst the tissues so 

 as to reach the situation in which they are ultimately 

 found ; but this opinion is scarcely tenable, however, 

 when it is considered that the ordinary seat of the 



p 



