diff --git a/test/speed.js b/test/speed.js
index 50fd3dc60..86663a237 100644
--- a/test/speed.js
+++ b/test/speed.js
@@ -5,31 +5,6 @@
   var objects = _.map(numbers, function(n){ return {num : n}; });
   var randomized = _.sortBy(numbers, function(){ return Math.random(); });
 
-  JSLitmus.test('_.isNumber()', function() {
-    _.isNumber(123);
-    _.isNumber(null);
-    _.isNumber(NaN);        
-    _.isNumber(/foo/);    
-    _.isNumber("abc");
-  });
-
-  JSLitmus.test('_.isString()', function() {
-    _.isString(123);
-    _.isString(null);
-    _.isString(NaN);        
-    _.isString(/foo/);
-    _.isString("abc");
-  });  
-
-  JSLitmus.test('_.isDate()', function() {
-    _.isDate(123);
-    _.isDate(null);
-    _.isDate(NaN);        
-    _.isDate(/foo/);
-    _.isDate("abc");
-    _.isDate(new Date());  
-  });  
-
   JSLitmus.test('_.each()', function() {
     var timesTwo = [];
     _.each(numbers, function(num){ timesTwo.push(num * 2); });
diff --git a/underscore.js b/underscore.js
index 46df7455e..7ae664386 100644
--- a/underscore.js
+++ b/underscore.js
@@ -30,6 +30,9 @@
   // Export the Underscore object for CommonJS.
   if (typeof exports !== 'undefined') exports._ = _;
 
+  // Create quick reference variables for speed access to Object.prototype.
+  var toString = Object.prototype.toString, hasOwnProperty = Object.prototype.hasOwnProperty;
+
   // Current version.
   _.VERSION = '0.5.0';
 
@@ -391,7 +394,6 @@
   /* ------------------------- Object Functions: ---------------------------- */
 
   // Retrieve the names of an object's properties.
-  var hasOwnProperty = Object.prototype.hasOwnProperty;
   _.keys = function(obj) {
     if(_.isArray(obj)) return _.range(0, obj.length);
     var keys = [];
@@ -477,18 +479,19 @@
   _.isUndefined = function(obj) {
     return typeof obj == 'undefined';
   };
-  
-  // have to define isNumber before _.each will work in IE
+
+  // isNumber needs to be defined before the rest of the isType functions,
+  // because _.each uses it in IE (and we want to use _.each for the closure).
   _.isNumber = function(obj) {
-    return Object.prototype.toString.call(obj) == '[object Number]';
+    return toString.call(obj) == '[object Number]';
   };
 
-  // Define the isArray, isDate, isFunction, isRegExp, and
-  // isString functions based on their toString identifiers.
+  // Define the isArray, isDate, isFunction, isRegExp, and isString functions
+  // based on their toString identifiers.
   _.each(['Array', 'Date', 'Function', 'RegExp', 'String'], function(type) {
-	var toString = Object.prototype.toString, typeString = '[object ' + type + ']';
+    var identifier = '[object ' + type + ']';
     _['is' + type] = function(obj) {
-      return toString.call(obj) == typeString;
+      return toString.call(obj) == identifier;
     };
   });
 
@@ -563,8 +566,7 @@
 
   // Add all of the Underscore functions to the wrapper object.
   _.each(_.functions(_), function(name) {
-    var unshift = Array.prototype.unshift,
-      method = _[name];
+    var method = _[name], unshift = Array.prototype.unshift;
     wrapper.prototype[name] = function() {
       unshift.call(arguments, this._wrapped);
       return result(method.apply(_, arguments), this._chain);