Sentence:  Also , interlobular air <WSD>drifts</WSD> may be all but nonexistent in the cow ; probably occur in the horse much as in the human being ; and , in contrast are present to a relatively immense degree on a segmental basis in the dog where lobules are absent ( Van Allen and Lindskog , ' 31 ) . 
Meaning of the word marked with <WSD> tags:  a force that moves something along