The html code in this Processing sketch is interfering with the html tags for preformatted code.
Please see the source code of this page for the original .ino sketch.

/*
 Beta Spectrum Web Server
 Context: Arduino Due
 Input pulses can be attached to any digital pin (max 3.3 V)
 
 */

#include 
#include 
#include 

EthernetServer server(80);

byte mac[] = {  
  0x90, 0xA2, 0xDA, 0x0D, 0xD5, 0x91 };
IPAddress gateway(194,47,126,33);
IPAddress subnet(255,255,255,224);
IPAddress ip(194,47,126,55);

const int inputLength = 16;
const int typeLength = 6;
const long checkInterval = 10000;
const int distanceAddress = 10;

char inputString[inputLength];
char requestTypeString[inputLength];
int nextChar = 0;
const int fileStringLength = 16;
char fileString[fileStringLength];
long resetTime;
int voltage = -100;

int inputPin = 22;
volatile int betaCounts = 0; // variable must not be stored in a register


// Initialize the Ethernet server library
// with the IP address and port you want to use 
// (port 80 is default for HTTP):

void setup()
{
  Serial.begin(9600);
  Serial.print("Initializing Ethernet connection... ");
  // start the Ethernet connection and the server:
  Ethernet.begin(mac, ip, gateway, subnet);
  server.begin();
  analogWriteResolution(12);
  analogWrite(DAC0, voltage);
  analogWrite(DAC1, 0);
  resetTime = millis();
  betaCounts = 0;
  pinMode(inputPin, INPUT);
  attachInterrupt(inputPin, incrementCounts, RISING);
}

void incrementCounts() {   // interrupt service routine
  betaCounts++;
}

void loop()
{
  String fileName = "";
  char inChar = 0;
  int requestType = 0;
  int requestedFileLength = 0;
  
  // listen for incoming clients
  EthernetClient client = server.available();
  if (client) {
    Serial.println("Got a client");
    TextFinder finder(client);
    while (client.connected()) {
      if (client.available()) {
        // look for whatever becomes before the /  (GET or POST)
        if(finder.getString("","/",requestTypeString,typeLength)) {
          Serial.print(requestTypeString);
          Serial.println(typeLength);
        }
        if(String(requestTypeString).startsWith("GET")) {        
          makeGETResponse(client);            
        }
        if(String(requestTypeString).startsWith("POST")) {
          finder.find("\n\r");  // skip the rest
          if(finder.find("millivolts")) {
            voltage = finder.getValue('=') % 4096;  // modulo for DAC range 
          }   
          makePOSTResponse(client);
         }

        // give the client time to receive the data
        delay(1);
        Serial.println("Closing the connection.");
        client.stop();
      }
    }
  }
  }

  
void makePOSTResponse(EthernetClient thisClient) { 
  thisClient.print("HTTP/1.1 200 OK\n");
  thisClient.print("Content-Type: text/html\n\n");
  thisClient.print("");
  thisClient.print("\n");
  // set up the body background color tag:
  thisClient.print(" \n");
  thisClient.print("
Beta spectrum experiment
 \n");
  thisClient.print("
Voltage setting changed to "); 
  thisClient.print(voltage);
  if (voltage < 0)
    {
      analogWrite(DAC0, 0);
      analogWrite(DAC1, -voltage);
    }
    else
    {
      analogWrite(DAC1, 0);
      analogWrite(DAC0, voltage);
    }
  delay(10);
  betaCounts = 0;
  resetTime = millis();
  thisClient.print("
 
Counter and timer reset; ");
  thisClient.print("return to controls 
");
  thisClient.println("");
}

void makeGETResponse(EthernetClient thisClient) {
  float time;
  time=(millis()-resetTime)/1000.0;
  thisClient.print("HTTP/1.1 200 OK\n");
  thisClient.print("Content-Type: text/html\n\n");
  thisClient.print("");
  thisClient.print("\n");
  // set up the body background color tag:
  thisClient.print(" \n");
  thisClient.print("
Beta rate experiment
");
  
  thisClient.print("
 \n");
  thisClient.print("
Current voltage: ");
  thisClient.print(voltage);
  thisClient.print(" mV 
");
  thisClient.print("
Current number of counts: ");
  thisClient.print(betaCounts);
  thisClient.print("; time elapsed since last reset: ");
  thisClient.print(time);
  thisClient.print(" seconds 
 \n");  
  thisClient.print("Voltage setting (range -4095 to 4095 mV): \n");
  thisClient.print("  
 \n"); 
  
  thisClient.print(" \n");
  // close the page:
  thisClient.println("\n");
  delay(1);
}