Sentence:  Any very systematic arrangement of the Sunday-school, that is, any strict assimilation of it to one or the other of our public systems, would, in particular localities, be its death blow. It would be beyond the grasp of the village conductor, grown old in other modes of teaching, and neither very willing nor very able to learn new ones; or, inapplicable to the fewness of the scholars; as, in other situations again, it would <WSD>losingly</WSD> substitute in the place of the numerous voluntary instructors, each having under his own wing his own little separated "flock", and bringing his attention to bear, with peculiar efficacy, upon this divided charge, large classes, with fewer instructors; and, as a necessary consequence, a less substantially beneficial influence. 
Meaning of the word marked with <WSD> tags:  In a manner that causes loss.