454 THE ANIMAL PARASITES OF MAN 



Moisture : Eggs and larvae do not live long under water, because 

 they suffocate or starve, but mature larvae will live for months (six to 

 twelve) in water ; they require no food in fact, can take none in 

 but live on their reserve granules, and in course of time become as 

 clear as glass. 



Thigmotropism : The mature larvae, after casting their skin, will 

 penetrate pith, climb up stems, stalks, etc., and creep into any pore. 



It is important to recognize that this third stage of the mature 

 larva is the only infective one. 



Mode of Entry into the Body. Infection is effected through the 

 mouth (Leichtenstern and others), and also through the skin, as was 

 first discovered by Looss and afterwards confirmed from the most 

 diverse quarters, partly in the case of Ancylostoma dnodeuale, 

 partly in that of A. caninuni in dog, man, and monkey. The 

 larvae that gain access to the intestine partly through contaminated 

 food, or through unwashed hands, or under some circumstances 

 through water, first throw off their " sheath " that is, they complete 

 moult II. Moult III takes place four to five days after they have 

 reached the gut, and they now have a mouth capsule supplied with 

 four small teeth arranged crosswise, enabling them to fasten on to 

 the intestinal epithelium, upon which they feed. On this food the 

 worms grow in four to six days to 3 to 5 mm. in length, and now 

 moult IV. takes place, thus attaining their definite shape and 

 distinctive character. About eight days later the sexual organs 

 commence to function ; at this time the first copulation should be 

 taking place it will later be frequently repeated and a few days 

 later the first ova are laid, first in less and later in larger numbers, so 

 that they appear in the faeces about four to five weeks after the 

 infection. 1 



Infection by the Skin. Mature larvae, which are placed on the 

 skin of man or suitable animals, cast their " sheath " and bore their 

 way through delicate fissures either horizontal in the superficial 

 scales of the epidermis, or through vertical fissures into hair follicles 

 where these exist, and then they invade the cutis. Now according 

 as they migrate further into the lymphatic vessels or the small vesicles, 

 the final path to the gut differs to some extent. The blood path 

 leads to the right heart, and from there into the lungs ; here the 

 larvae leave the blood stream and enter the air passages, over the 

 mucosa of which they travel further headwards, through the bronchi 

 into the trachea and larynx, and from hence through the oesophagus 

 to the stomach ; in some cases also they are swallowed. The 



1 From the number of eggs present in a given quantity of faeces, the number of female 

 Ancylostomes present in the gut can be reckoned by a formula of Leichtenstern's (x = 4 . f in 

 which a signifies the number of eggs counted in a single gramme of fceces). 



