If you are taking an author’s own words you must indicate this by using quotation marks and show where the words came from. Here is a sample:
“Doctors’ deep suspicion of what they read in the newspapers and even in the less-carefully edited of the medical journals, helps to explain some of the early skepticism about insulin in countries like Britain” (Bliss, 1982, p.190).
Even if you use your own words to express the same idea you still must cite your source. For example, if you were to paraphrase the above idea you might say something like this:
Insulin as a treatment for diabetes was not widely accepted at first because doctors found it hard to believe in the legitimacy of medical discoveries as reported both by newspapers and by some less academic medical journals (Bliss, 1882, p.190).