There's nothing at that Internet page to tell you where the excerpt came from -- you just have to know it's from Innocents Abroad. But assuming that you do know that, you could search the web for the title if you want more of the book. A better choice would be to go to about.com (http://about.com/) and use that site's internal search engine -- just type in "mark twain" (without the quotation marks and all lower case, of course) and you will be transferred to a page where you will find a link to a "Mark Twain Guide Site." There's someone working for about.com who's a Mark Twain expert!
Click on that link and you will soon be at the Guide Site, http://marktwain.about.com/arts/books/marktwain/mbody.htm?COB=home&PM=112_100_T) where you can click on the "Etexts: Books" link in the left sidebar. You will then go to a page that page links to all the available Mark Twain books that are on line in full text (http://marktwain.about.com/arts/books/marktwain/msub1.htm).
Click on Innocents Abroad and you are where you want to be: http://marktwain.about.com/arts/books/marktwain/gi/dynamic/offsite.htm?site=http://etext.lib.virginia.edu/etcbin/toccer%2Dnew%3Fid=TwaInno%26images=images/modeng%26data=/texts/english/modeng/parsed%26tag=public. That last is a ridiculously long URL, but you don't have to type it in -- just follow the links in this tip and you're there.
Along the way you will have noticed that all the other Mark Twain books which you always wanted to read are also available free of charge on the Internet. Early on, Twain made fun of money-grubbers, but, after a tough and adventurous life, he became successful and was a money-grubber himself: he would have protested vigorously the free aspect of the Internet -- at least as far as his own books were concerned. We have no such prejudices ourselves, and so we are perfectly willing to read whatever is out of copyright and available on the net. There are links to thousands (yes, thousands) of free eTexts at http://www.mmdtkw.org/literature.html.