240 EVOLUTION 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 
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, 
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 ‘‘ 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 
