diff --git a/src/disease.rs b/src/disease.rs
index fe49ddf..832c9cf 100644
--- a/src/disease.rs
+++ b/src/disease.rs
@@ -5,14 +5,14 @@
 
 // #[derive(Debug)]
 pub struct Disease {
-    pub infection_rate: u32,
-    pub curing_rate: u32,
-    pub death_rate: u32,
-    pub traits: Vec<u32>,
+    pub infection_rate: i32,
+    pub curing_rate: i32,
+    pub death_rate: i32,
+    pub traits: Vec<i32>,
     pub name: String,
 }
 impl Disease {
-    pub fn new(infection_r: u32, curing_r: u32, death_r: u32, the_name: String) -> Self {
+    pub fn new(infection_r: i32, curing_r: i32, death_r: i32, the_name: String) -> Self {
         Self {
             infection_rate: infection_r,
             curing_rate: curing_r,
diff --git a/src/population.rs b/src/population.rs
index 328de34..9b368c4 100644
--- a/src/population.rs
+++ b/src/population.rs
@@ -6,29 +6,10 @@ pub struct Point {
     y: i32,
 }
 
-#[derive(Debug)]
-struct Stats {
-    normal: i32,
-    infected: i32,
-    immune: i32,
-    dead: i32,
-}
-
-impl Stats {
-    fn new() -> Stats {
-        Stats {
-            normal: 0,
-            infected: 0,
-            immune: 0,
-            dead: 0,
-        }
-    }
-}
-
 pub struct Population {
-    pub start_infected_ratio: u32,
-    pub start_immune_ratio: u32,
-    pub start_dead_ratio: u32,
+    pub start_infected_ratio: i32,
+    pub start_immune_ratio: i32,
+    pub start_dead_ratio: i32,
     pub humans: Vec<Human>,
     pub width: i32,
     pub height: i32,
@@ -40,32 +21,12 @@ pub fn human_idx(x: i32, y: i32, width: i32) -> usize {
     ((y * width) + x) as usize
 }
 
-fn humans_stats(humans: &Vec<Human>) -> Stats {
-    let mut stats: Stats = Stats::new();
-    for human in humans.iter() {
-        match human.present_state {
-            State::Normal => {
-                stats.normal += 1;
-            }
-            State::Infected => {
-                stats.infected += 1;
-            }
-            State::Immune => {
-                stats.immune += 1;
-            }
-            State::Dead => {
-                stats.dead += 1;
-            }
-        }
-    }
-    stats
-}
 
 impl Population {
     pub fn new(
-        start_infected_ratio: u32,
-        start_immune_ratio: u32,
-        start_dead_ratio: u32,
+        start_infected_ratio: i32,
+        start_immune_ratio: i32,
+        start_dead_ratio: i32,
         width: i32,
         height: i32,
         plague: Disease,
@@ -313,9 +274,13 @@ impl Population {
     // }
 }
 
-pub fn roll(probability: u32) -> bool {
-    let mut rng = rand::thread_rng();
-    rng.gen_range(0..CORRECTED_PERCENTAGE) <= probability as i32
+pub fn roll(probability: i32) -> bool {
+    if probability > 0 {
+        let mut rng = rand::thread_rng();
+        rng.gen_range(0..CORRECTED_PERCENTAGE) <= probability
+    } else {
+        false
+    }
 }
 
 #[cfg(test)]
@@ -323,6 +288,46 @@ mod tests {
     use super::*;
     use parameterized::parameterized;
 
+    #[derive(Debug)]
+    struct Stats {
+        normal: i32,
+        infected: i32,
+        immune: i32,
+        dead: i32,
+    }
+
+    impl Stats {
+        fn new() -> Stats {
+            Stats {
+                normal: 0,
+                infected: 0,
+                immune: 0,
+                dead: 0,
+            }
+        }
+    }
+
+    fn humans_stats(humans: &Vec<Human>) -> Stats {
+        let mut stats: Stats = Stats::new();
+        for human in humans.iter() {
+            match human.present_state {
+                State::Normal => {
+                    stats.normal += 1;
+                }
+                State::Infected => {
+                    stats.infected += 1;
+                }
+                State::Immune => {
+                    stats.immune += 1;
+                }
+                State::Dead => {
+                    stats.dead += 1;
+                }
+            }
+        }
+        stats
+    }
+
     #[parameterized(x = {
         2, 3, 5
     }, y = {
@@ -429,9 +434,10 @@ mod tests {
     }
 
     #[parameterized(rate = {0, 100}, expected = {false, true})]
-    fn roll_test(rate: u32, expected: bool) {
+    fn roll_test(rate: i32, expected: bool) {
         let tries = 1000;
         let mut result = 0;
+        println!("Testing roll, rate {}, expected {}", rate, expected);
         for _x in 0..1000 {
             if roll(rate) == expected {
                 result += 1;
@@ -442,8 +448,8 @@ mod tests {
 
     #[parameterized(infection_rate = {0, 100, 0}, death_rate = {0, 0, 100}, infected_expected = {0, 1, 1})]
     fn propage_test(
-        infection_rate: u32,
-        death_rate: u32,
+        infection_rate: i32,
+        death_rate: i32,
         infected_expected: i32,
     ) {
         let disease: Disease;