Based on the given sentence above, I can say that the complete sentence is "The air". When we say subject of the sentence, this is the one that is being talked about in the sentence. In other words, it is the topic. A subject can either be simple or complete. For a simple subject, it only consists of the main noun. For complete subject, this includes the modifiers of the noun. Hope this helps.
Jekyll's letter in the excerpt from The Strange Case of Dr. Jekyll and Mr. Hyde reveals that D. Jekyll is in a desperate situation and needs help from Lanyon.
