REPRODUCTION AND GROWTH 169 



frog, we should certainly say that these two things were distinct 

 kinds of animals. As it is we know, from continued observation, 

 that they are the same animal. 



Normal, ordinary organic growth then resolves itself into the 

 study of development. 



60c. Organic Repair and Regeneration. Growth exhibits 

 itself in the processes of repair and regeneration. A wound 

 normally heals in such a way that the former structure of the 

 injured parts is restored. The injured tissues grow, but they 

 differentiate at the same time, for examination of the " proud 

 flesh " in a wound shows that this has not the structure of the 

 tissues that are going to be repaired. As the cavity of the wound 

 fills up, however, the proud flesh (granulation tissue) takes on the 

 forms of the muscles, blood-vessels, bone, etc., that were injured 

 and these new tissues arrange themselves in those ways in which 

 the former tissues were arranged before the injury occurred. 



Therefore the parts of the body that grew in order to repair 

 damage caused by the accident contained the agency called the 

 organization. This operated by taking chemical materials from 

 the blood, by chemically changing these materials and by rearrang- 

 ing the changed materials in a structure of connective tissue, 

 muscle, blood-vessels, etc. The plan of this structure was in the 

 organization, in the sense that the latter operated in such a way 

 as to realize it. 



6od. Regeneration is repair on the large scale. The power 

 of repair exhibited by a complex animal, such as man, is very 

 limited. Wounds, in the ordinary sense, can heal up, but an 

 extensive part of the body, such as a leg, that is destroyed by 

 accident, cannot be replaced. In the structurally simpler animals, 

 such as Crustacea, this extensive power of repair is possessed. 

 When a crab loses a limb by accident (or voluntarily, by the 

 curious process called " autotomy ") a little *' bud " forms at the 

 stump of the lost limb. This grows and the growing parts 

 differentiate in such a way as to re-form the lost limb. Here the 

 organization can effect far greater changes than it can in the case 

 of the structurally more complex mammalian animal. 



6oe. Malignant, or Sinister Growth. A form of growth 

 that is called " mahgnant " is exhibited by those structures called 

 " tumours," " cancers," etc. In such structures, things that 

 " ought not " to be there are present in the body of an animal. 



