42 E nsheathed Larvae of some Parasitic Nematodes 



He meets the obvious criticism that these are not cases of skin in- 

 fection by the following: "On pourra nous objecter que la faculte 

 presentee par les larves infectieuses de certains Nematodes de penetrer 

 dans le cordon ombilical ne prouve pas qu'elles soient susceptibles de 

 traverser la peau." 



In view of my own results detailed above I have no hesitation in 

 claiming that the ensheathed larvae of T. relorlaeformis from the rabbit 

 can be ruled out of the list of skin penetrators. 



EFFECTS OF TEMPERATURE. 



The behaviour of ensheathed larvae of G. slrigosum and T. relorlae- 

 formis was so markedly different from that of N. americanus when 

 applied to the skin at 37° C. that I determined to test the matter further. 



For this purpose I used an electric warm stage in which a slide 

 carrying a drop containing larvae can be placed and the temperature 

 gradually raised from room temperature to 37° C. In this way I was able 

 to watch the reaction of the larvae to the rise in temperature and to 

 determine fairly well the optimum temperature for greatest activity. 

 The result is shown in the accompanying table. 



Grajphidiuni slrigosum and Trichoslrongylus relortaeformis. 



Temperature Remarks 



22-23° C. Larvae showing good motility 

 23-24 Very active 



24-25 Very active at edge of drop 



25-26 1 or 2 showing coiling movement, rest actively motile. 



26-27 A few showing sharp spasmodic backward and forward bending, rest 



wriggling actively 

 27-28 A few coiling and uncoiling, rest actively motile 



28-30 Those coiled remained coiled longer, about half coiled, rest active 



30-31 More than half coiled 



31-32 A few moving actively, rest coiled and remaining so, I or 2 straight and 



motionless except for an occasional movement of one end 

 34 1 or 2 active, the rest coiled or straight and motionless 



35-5 Only one moving, rest as at 34° C. 



36-6 No movement 



From the above it can be seen that the optimum temperature for 

 greatest activity is between 22° and 25° C. At 25° C. coiling begins to 

 take place and by the time normal body temperature is reached practi- 

 cally all motiUty has ceased. 



This is a curious fact and not easy to understand when one remembers 

 that the larvae require for their further development to get into the 

 alimentary tract of the host where, of course, they will be permanently 

 at 37° C. 



