264 PARASITES OF THE DOMESTIC ANIMALS 



are swallowed and reach the outside with the feces. Further than this 

 little is laiown as to their life history. The larvae do not appear to pass 

 through any stages of development in the bronchi of their host, the first 

 phases of their existence probably requiring that they be expelled from 

 the animal. 



Having reached the outside, if the larvae encounter sufficient warmth 

 and moisture, they molt and this is later followed by a second molting 

 after which they retain their coverings and in this condition may resist 

 desiccation for a long time. It is probable that the larvae find their 

 way to a host with the wet grass and, especially in the case of sheep, 

 with collections of water upon the pastures which the animals drink. 

 The view as to direct development and infection is supported by the 

 investigations of Romanovitch and Slavine (p. 256), and it seems 

 probable that in all cases of bronchial and pulmonary strongylosis the 

 infection is direct. Some authors, however (Cobbold, Leuckart), be- 

 lieve that a portion of the larval stage is lived in an invertebrate host, as 

 an earthworm, larval insect, or mollusc. 



The larvae are usually taken up by the host animals in the spring, 

 though it is probable that infection may occur at any time during the 

 pasture season. That infection cannot occur directly from animal to 

 animal has been demonstrated by Leuckart, Herms and Freeborn and 

 others who were not successful in bringing it about by the introduction 

 into the respiratory passages and stomach of bronchial mucus containing 

 numerous embryos. 



The course of the larval worms in reaching the bronchi after natural 

 infection by way of the digestive organs has not been demonstrated. 

 Based upon the function of rumination and the peculiar susceptibility 

 of ruminating animals, the invasion of the air passages has been attrib- 

 uted to the regurgitation of contaminated food, the worms passing 

 from the pharynx to the larynx and trachea. But this hypothesis seems 

 to have no more than plausibility in its support, and certainly cannot 

 well apply to the case of the non-ruminating hog. 



Control. — In districts where bronchial and pulmonary strongylosis 

 prevails, low, marshy and wet pastures or parts of pastures should not 

 be accessible to susceptible animals. Drainage and a liberal covering 

 of the ground with lime phosphates will do much to destroy the larvae. 

 Bearing in mind that young animals are more susceptible to attack than 

 older ones, it is advisable where the disease prevails to give them feed 

 and water each day before they are turned upon pasture. This will in a 

 measure prevent them from going to pools and marshy places for water 

 where they are likely to linger and graze unless their night's fast has 

 been previously somewhat broken. Where hogs and cattle are con- 

 cerned the pens, stables and drinking places should be repeatedly cleaned 

 and disinfected. Sputum, feces and bedding are not to be placed 



