128 



believes that the clinical form of the malady may be in agree- 

 ment with the stage of evolution of the parasite. 



There appears to be very little evidence to support 

 Railliet's theory, viz., that the lesions are due to the penetra- 

 tion of the skin by embryos which develop as erratic parasites 

 in an abnormal situation in undergoing an analagous develop- 

 ment to that which they accomplish normally in the body of 

 the fly. It has been shown experimentally that the final larval 

 stage can produce a typical reaction, go, at least, this aberrant 

 development does not appear to be necessary. 



It is possible that embryos may either penetrate the skin 

 or become lodged in sores, where they may set up a tissue 

 reaction, but there is no experimental evidence to support 

 this assumption. 



Even if we assume the possibility of embryo6 of 

 Habronema setting up a certain type of lesion in the skin, 

 there appears to be little or no evidence to suggest that such 

 embryos are capable of developing through their larval stages 

 in this situation. Further, there is no proof that the embryos 

 found by Ercolani in the one case, and by Buffard in the other, 

 are embryos of Habronema. 



Embryos of Habronema are to be found in the faeces at 

 all times of the year. If these embryos leave the faeces, and 

 in penetrating the skin and their subsequent evolution they set 

 up a typical "summer sore," it is difficult to explain (1) the 

 seasonal occurrence of the tumours and (2) the massive infec- 

 tion at one point. 



The life-history of the three species of Habronema is of 

 that type which involves a simple alternation between two 

 hosts — one a vertebrate harbouring the adult and the other an 

 invertebrate harbouring the larval stage. From a theoretical 

 consideration it seems reasonable to assume that it is improb- 

 able, should this alternation be broken, that the worm would 

 be able to carry on its development. 



Before Railliet's theory can be accepted it will require the 

 support of more clinical and experimental evidence. 



The "inconstant parasite" of Descazeaux, believed by 

 Railliet to be an early larval form of Habronema resembling 

 stage 2 of H . muscae as described by Ransom, is not definitely 

 a larval Habronema. It was described by Descazeaux as a 

 "larve strongyloide." He described the anus as being open 

 and situated at the base of the tail and a vulva situated at 

 the posterior third of the body. The larva is 900 to 950 fx 

 long by 25 /jl broad. It will be seen that the larva is approxi- 

 mately only half the width of a Habronema larva. From an 

 early stage resembling that of stage 1 of Ransom the growth 

 of Habronema larvae is mainly in length, the width or 



