"the matriculant is now a full-fledged student, free to come and go at will. Absolutely no restrictions are placed upon him, he may attend all lectures or no lectures. He wears no academic dress, he lives in no dormitory." -------- This was true mostly all the way up until the bachelor reforms in the 2000s. Nowadays, there are quite a lot of classes that you have to sit in (depends a lot on the university and courses)
" But every German class-hour has its “academisches viertel” or quarter-hour of grace." -------- We basically still "have" this in a way but it basically only means that many courses start at quarter past x (e.g. 8:15).
"Then the professor enters in haste. Before he has even reached his desk, he begins, “Meine Herren und Damen!” (the order is significant)" -------- Nowadays, it's the other way around ("Meine Damen und Herren").
"Occasionally scraping of feet, “Scharren,” a well-known signal, warns the lecturer that his words are not heard at the rear of the room, and he raises his voice, until the shuffling ceases." -------- This is not common anymore, as far as I know. A shame (well, we are allowed to raise our voices and tell the prof to talk louder, which works as well).