2 4 o E VOL UTION AND DISEASE. 



manner in which these tumours destroy life, clearly 

 coincide with what is positively known with regard to 

 infective granulomata. The fact that sarcomata make 

 up the greater part of tumours occurring in wild and 

 domesticated animals has, in my opinion, a very signifi- 

 cant import in this relation. 



NEOPLASMS. Tumours belonging to this group will 



A not detain us long. They are innocent in so far as the life 

 of the individual is concerned, and are composed of fat, 

 bone, or cartilage ; in some cases they consist of an 

 aggregation of blood or lymph vessels. Such tumours 

 may cause inconvenience from their large size, or inter- 

 fere with vital organs, but they never produce constitu- 



\ tional disturbance or infect the system. In many 

 instances they occur as local overgrowths of tissues, 



1 resembling in this way the deviations which occur in 

 the vegetable world and known as " sports ; " this term 

 being used by gardeners as signifying a bud or off-shoot 

 which suddenly assumes a new, and sometimes very 

 different, character from that of the rest of the plant. 

 The term u spontaneous variation " is sometimes applied 

 to such conditions. As " sports " occur throughout the 

 plant world, so simple neoplasms occur throughout the 

 vertebrate kingdom, and wherever fat, bone, and cartilage 

 are found, will the tendency to " sports " exist and pro- 

 duce fatty tumours, bony tumours, cartilaginous tumours, 

 and the like. 



Cohnheim attempted to account for the occurrence of 

 neoplasms by supposing that during the development of 

 an animal a certain number of the original cells of a 

 part remained undeveloped, and that later in life they 



