Was reading the air cell parts of the first page and then I followed the links to this: 
https://www.backyardchickens.com/t/39604/some-causes-of-early-chick-mortality, and now I am having google disease. Where you are sure your suffering from whatever horrible thing you find on Dr Google. The chicks from this batch of Welsummer hatched eggs all died but one. The ones that hatched and died all had labored breathing, chirping and death. The one had green liquid bubbling out of its mouth. The last one to die with the yolk sack that would never absorb had white poop come out right before she started gasping and died. So now I am freaking myself out. 
 And the lone survivor doesn't look well to me now. Won't eat, won't drink and chirps non stop, sleep standing up and wakes every few seconds. Gah!
b) Pullorum
It is an acute infectious and fatal bacterial disease of chicks characterized by ruffled feather, white diarrhea, labor breathing, chirping and death.