PATHOLOGY: E. F. SMITH 
445 
to that of cancer in man and animals, some allowance, of course, being 
made for differences in the structure and development of plants. My 
concept is this, that fundamentally plants and animals are alike, that 
physical and chemical laws apply equally, that is uniformly, to all 
living things, and hence that discoveries relative to the fundamental 
cell-mechanics of animals apply equally to plants, and vice versa. ^ 
If cancer occurs in plants and is due to a parasite, as I maintain, then 
cancer in man must also be due to a parasite, and since I show that 
several kinds of plant cancers are due to the same organism, the differ- 
ences being due solely to unlike tissue reactions, we may anticipate the 
same thing to be true in man, and search for one parasite rather than 
many. 
2. Human and animal tumors for which no cause has been discovered. — ■ 
These tumors fall readily into two groups which intergrade more or 
less. These are (a) encapsuled benign tumors, and {h) free-growing 
mahgnant tumors or cancers. I will here consider only the malignant 
tumors. There are several t3^es of these; the simplest and the com- 
monest being proliferations (1) of the connective tissues, resulting in 
fleshy tumors known as sarcomas, and (2) of the various kinds of epithe- 
lium, resulting in eroding tumors known as carcinomas. In addition to 
tumors of the brain and nervous system, which are sometimes malig- 
nant but which may here be left out of account, there are (3) very curi- 
ous tumors containing mixed tissue elements of two germ layers (con- 
nective tissues, cartilage, striped and plain muscle-fibres, glandular 
tissue, etc.) some of which are benign while others are extremely mahg- 
nant, and finally, (4) embryonal teratomas which, in addition to the 
cancerous element, contain numerous foetal fragments, derived from all 
three of the primitive germ layers, often a great variety of tissue-frag- 
ments, variously fused and jumbled, but all embryonic and never com- 
ing to maturity. 
The leading characteristics of these cancerous tumors are (1) Un- 
limited cell proliferation emancipated from bodily control; (2) Appear- 
ance of destructive secondary tumors, often in vital organs, which tumors 
are derived from the primary tumor either by development from dis- 
lodged creeping and floating tumor cells, or by uninterrupted growth 
from a chain of tumor cells originating in the primary tumor. These 
secondary tumors wherever they are developed repeat more or less 
closely the structure of the parent tumor. Add, to these manifestations, 
(3) a destructive action on surrounding tissues, which are crushed, ab- 
sorbed or poisoned, and we have in brief the main phenomena of can- 
