330 



THE ANIMAL PARASITES OF MAN 



Leichtenstern conducted unimpeachable experiments on human 

 beings, which proved that infection takes place through the direct 



introduction of these 

 larvae. When the cir- 

 cumstances under which 

 miners and brickmakers 

 work are taken into con- 

 /\V ; sideration the frequency 



of the infection is easily 

 understood, and as in 

 above - ground occupa- 

 tions the ova, and, of 

 course, also the larvae, 

 perish during winter 

 from the effects of the 

 cold, conditions are far 

 more favourable to the 

 worm in the deeper, 

 and therefore warmer, 

 mines. 1 



Looss, who succeeded 

 in infecting young cats 

 and dogs, studied the 

 metamorphosis which 

 the larvae go through 

 within their host (fig. 

 216) ; it is completed 

 in three stages. The 

 larvae pass through the 

 stomach of the exper- 

 imental animals com- 

 paratively quickly, yet 

 hardly grow any longer 

 during the first days ; 

 on about the fifth day 

 the signs of a future 

 moult become appa- 



FIG. 2 1 6. Ankylostoma duodenale. On the left, 

 four days after transmission into the dog 190/1 ; 

 in the middle at the commencement of the 

 second stage of development (five to six days), 

 105/1 ; on the right fourteen to fifteen days after 

 infection, 42/1. (After Looss.) 



1 There is no relation at all between the Ankylostoma duodenale and horses, such as 

 Rathonyi strives to prove (Dtsch. Med. Wchschr., 1896, No. 41), the author is the victim 

 of an error ; the supposed ova and larvae of Ankylostomum, which he found or culti- 

 vated in the excrement of horses, originated from Sclerostomum tetracanthum and 

 Scl. equinum (Railliet, A., in C. R. soc. bioL, Paris, 1897 [10], iii., p. 1132 ; Ratz, St., 

 v. in C. f. B. P. u I., 1898 [i], xxiv., p. 298.) 



