diff --git a/lib/fhir_models/bootstrap/common_definitions.rb b/lib/fhir_models/bootstrap/common_definitions.rb
index c7a5a200..a240ca54 100644
--- a/lib/fhir_models/bootstrap/common_definitions.rb
+++ b/lib/fhir_models/bootstrap/common_definitions.rb
@@ -10,22 +10,30 @@ def self.included(base)
     module ClassMethods
       extend FHIR::Deprecate
 
+      def ig_resources
+        @ig_resource ||= @ig_loader.load
+      end
+
+      def cache
+        @cache ||= {}
+      end
+
+      # This method actually just sets up lazy loading to avoid having to load
+      # everything at start time.
       def load_igs(ig_file_name)
-        ig_loader = FHIR::Generator::IGLoader.new(ig_file_name)
-        @ig_resources = ig_loader.load
-        @cache = {}
+        @ig_loader = FHIR::Generator::IGLoader.new(ig_file_name)
       end
 
       def find_structure_definition(structure_defs, target_name)
         return nil if target_name.nil?
-        return @cache[target_name] if @cache[target_name]
+        return cache[target_name] if cache[target_name]
 
         definition = structure_defs.find do |sd|
           sd['id'] == target_name || sd['name'] == target_name || sd['url'] == target_name
         end
 
-        @cache[target_name] = create_structure_definition(definition) if definition
-        @cache[target_name]
+        cache[target_name] = create_structure_definition(definition) if definition
+        cache[target_name]
       end
 
       def create_structure_definition(definition)
@@ -39,12 +47,12 @@ def create_structure_definition(definition)
       # # ----------------------------------------------------------------
 
       def primitive_types
-        @ig_resources.primitive_types
+        ig_resources.primitive_types
       end
       deprecate :get_primitive_types, :primitive_types
 
       def complex_types
-        @ig_resources.complex_types
+        ig_resources.complex_types
       end
       deprecate :get_complex_types, :complex_types
 
@@ -58,7 +66,7 @@ def type_definition(type_name)
       # ----------------------------------------------------------------
 
       def resource_definitions
-        @ig_resources.resource_definitions
+        ig_resources.resource_definitions
       end
       deprecate :get_resource_definitions, :resource_definitions
 
@@ -68,7 +76,7 @@ def resource_definition(resource_name)
       deprecate :get_resource_definition, :resource_definition
 
       def extension_definition(extension_name)
-        find_structure_definition(@ig_resources.extension_definitions, extension_name)
+        find_structure_definition(ig_resources.extension_definitions, extension_name)
       end
       deprecate :get_extension_definition, :extension_definition
 
@@ -76,7 +84,7 @@ def extension_definition(extension_name)
       def basetype(uri)
         return nil if uri.nil?
 
-        defn = @ig_resources.profiles.detect { |x| x['url'] == uri } || @ig_resources.extension_definitions.detect { |x| x['url'] == uri }
+        defn = ig_resources.profiles.detect { |x| x['url'] == uri } || ig_resources.extension_definitions.detect { |x| x['url'] == uri }
         return nil if defn.nil?
 
         defn['type']
@@ -85,14 +93,14 @@ def basetype(uri)
 
       # Get the StructureDefinition for a given profile.
       def profile(profile_url)
-        find_structure_definition(@ig_resources.profiles, profile_url)
+        find_structure_definition(ig_resources.profiles, profile_url)
       end
       deprecate :get_profile, :profile
 
       def profiles_for_resource(resource_name)
         return nil if resource_name.nil?
 
-        @ig_resources.profiles.select { |x| x['type'] == resource_name }
+        ig_resources.profiles.select { |x| x['type'] == resource_name }
       end
       deprecate :get_profiles_for_resource, :profile_for_resource
 
@@ -101,18 +109,18 @@ def profiles_for_resource(resource_name)
       # ----------------------------------------------------------------
 
       def valuesets
-        @ig_resources.get_value_sets
+        ig_resources.get_value_sets
       end
 
       def get_codes(url)
-        @ig_resources.get_codes(url)
+        ig_resources.get_codes(url)
       end
 
       # Why do we have this function?
       def get_display(system, code)
         return nil if system.nil? || code.nil?
 
-        @ig_resources.get_value_sets.each do |value_set|
+        ig_resources.get_value_sets.each do |value_set|
           if value_set['expansion'] && value_set['expansion']['contains']
             value_set['expansion']['contains'].each do |contain|
               return contain['display'] if contain['system'] == system && contain['code'] == code
@@ -132,7 +140,7 @@ def get_display(system, code)
       # ----------------------------------------------------------------
 
       def self.search_parameters(type_name)
-        @ig_resources.get_search_parameters(type_name)
+        ig_resources.get_search_parameters(type_name)
       end
       deprecate :get_search_parameters, :search_parameters
     end