[MUSIC] Now let's come to the third guide of the story, Salvador E Luria. Salvador E Luria was born Salvatore Luria in Torino Italy from a intellectual Jewish family. His parents wanted him to become a physician, so he studied medicine. He hated it. He was a very shy, very reserved, very withdrawn kind of person. And just single disgusting thing that you have to see in the hospital was not for him. He was too depressed to become a psychiatrist, otherwise that would have been his choice but he hated medicine, and so as soon as he got his medical degree, he left his family. He went to Rome to work as an assistant in a physics lab. Now, imagine the courage of the physics lab P,I. Principal Investigator Professor. You have this guy who has done physics in the first year of medical studies which is a micron thick. And this guy want to be hired as an assistant in an experimental physics lab. That takes a lot of courage to hire somebody like this. And so as Eddie takes him he works, no problem but then a year later he was planning to go and meet Dellbrook in 38 but Italian government has new racial laws that prevent Jews from having official jobs, working at an institute as scientists. So he has to leave. He has to leave, okay. So where does he go? He goes to Paris, because Paris is close. Francis, okay. So he goes to Paris, and there he meets, the Volmann family. Which we will re, see again later on in the course. The Volmann parents are working in institute Pastel, they're working on lysogene, the strange phenomenon that we will discuss later on. And their son becomes a good friend of Luria and they go together bicycling in Normandy and then of course the war starts. So again Luria is not stupid. He knows perfectly well that the anti Jewish laws of Fascist Italy is nothing compared to the anti-Jewish laws of Nazi Germany. So it goes away, managed to get a boat and come to the states and he's offered a job as an assistant in biology at Columbia. And that's where he will meet Delbruck. So they will meet in 1940, December 1940, the 29th of December 1940. Delbrook has heard about Luria and he goes to visit him at Columbia. In the mean time Luria when he landed in the US, has finally fulfilled one of his dreams. This guy hated his first name Salvatore. He really hated it. So he's asked by the immigration officer in the US what's your first name, and so he changes it. Salvador, Salvador sounds more Spanish, more flamboyant. And then the immigration official typically asking middle name, middle initial And he's at loss. He has no idea what middle initial to use, so he used the E of Salvatore. So that's how Luria becomes Salvador E Luria. The E means nothing but the last letter of the Salvatore. So they meet and they're extremely excited of a doing experiment with this phage. And Delbruck has not yet started to work with phage. But they see that it can be a simple organism. Which means a simple genetic structure. So when they do that, and I just have to find where it is. Okay, so that night, two days before January 1st 1941. So America still not yet and has not yet entered the war. So after their first meeting, Max takes Delbruck to dinner with two other scientists. Two other physicists. One of them being Woflgang Pauli. So you imagine young Luria meeting Pauli. And the first thing that Pauli ask him is [FOREIGN]. And then he turns around and started eating. And started talking in German. Full speed. Of course, Lurai doesn't understand a word of it. He's completely lost. And he's very, very scared because he knows that one of the famous quotes was that so young and he has already contributed so little, which is devastating for a young man. So Delbruck is dominant, Delbruck is outgoing, Luria is withdrawn, but somehow they get along. I don't think they really understand each other. Lurai writes a book on bacterial genetics, sends the first copy to. And a few months later, he asked did you get my mail. And says, your book. These is an error in the footnote of page 34 that was a comment, the only comment. Lurai was deeply, deeply hurt, but that was. So goes to Max and says, Max, I've thought of a wonderful experiment. And Max immediately, the experiment to end all thinking? He was devastating. He was devastating in science, he was devastating in normal life. At summer 41 they go to Cold Spring Harbor together to do an experiment on phage and Max decides that they will have to go and play tennis. Okay? Lurai has never played tennis. Lurai is clumsy, he's short sighted. He's the typical anti sport. But Max said we go and play tennis, so he goes after five minutes, Max explode, why don't you learn enough to play with grownups. I mean these are full adults and they treat each other in such terrible way. The experiment they had in mind which is the basis of the paper we're going to read. Is the following. We know that when a phage, a bacterial phage, a bacterial virus infects a bacterium, it's like a black box. And then 20 or 30 or 40 minutes later, the black box explodes, and liberates a progeny of let's say 100 phage. Sometimes 50, sometimes 300. So they know that sub-phage. Lies in 20 minutes and some phage lies in 40 minutes. So their idea which may seem completely childish, but remember there was not much information available at the time. Their idea is that they're going to co-infect a bacterium with a slow virus and a fast virus. When the fast virus will lyse the cell, after 20 minutes, the slow virus would have not yet reached the final stage, but it will have reached an intermediate stage. And so you will trap in the test tube an intermediate in the assembly of, or in the production of the virus. That's the general idea. So for that, they needed first virus. Delbrück was extremely clumsy with his hands. Luria had some training as an MD, and he was more practical. And so he would do the experiment. And basically, Max would watch over his shoulder. And there's, there's actually a picture showing Delbrück watching over the should of Luria during a experiments. It's absolutely true. And they didn't mind because their mind was so different that he could accept to discuss practically as equal. So in order to do that they wanted to be able to count the slow virus and the fast virus. Now, there are lots of ways you could think of doing that but the best way of doing that would be to have a bacterium that is resistant to virus A and sensitive to virus B, and another bacterium mutant that is resistant to virus B and sensitive to virus A. So using these two hosts, you can count the A virus and the B virus, separately, independently, so that's the idea of the experiment. So is it possible to get a bacterium that is resistant? Well, it had been noticed a long, long, long time ago well, 20 years before. That's when you infect a culture of bacteria, of sensitive bacteria with a virus. The first thing you see is that the virus will lyse the culture. Lyse the culture means that instead of being turbid, it becomes clear. That's what lyses mean all the bacteria have been killed. Fine. What people noticed is that if you leave your sample on the bench, if you throw it away immediately, you've lost. But if you're a little bit clumsy and you leave things on the bench just in case, and not clean up. You're not a maniac of cleaning you desk and you bench. If you do that and that happened, sometimes the culture becomes turbid again, and it's not because you've put some dirt into the tube you haven't opened the tube, but all of a sudden, the tube is turbid again. Some bacteria has grown where there was none before. So you start with a population of bacteria, all derived from the same ancestor. They all sensitive to the phage. They all die. All but one or two and these one or two survive and multiply. That's what's called the secondary growth. So they knew it was possible to isolate, actually they called it virus resistant mutant. The same as if you miss some receptor on the surface of our cells, we're resistant to some infection. Some people are resistant to HIV because they dont have a protein called CCR5 on the surface of the lymphocyte. So they resist to the infection. So it's something very classical.