CANCER, ITS COURSE AND ITS CAUSES 



By 



Leo Loeb 



Cancer is a disease wliicli differs very markedly in its 

 character from all other diseases. It is common to man 

 and to higher animals and in a few cases something analo- 

 gous to it has been found also in invertebrates. In gener- 

 al, the character of the disease and its course are the 

 same, wherever it appears, and in order to bring out this 

 distinct character we are led to compare it with certain 

 infectious diseases such as tuberculosis and diphtheria. 



In tuberculosis a microscopic organism, the tubercle 

 bacillus, enters the body usually through the respira- 

 tory tract or through the intestines. Wherever a few 

 tubercle bacilli settle, they set up a certain reaction on 

 the part of the host tissue. The cells nearest to the 

 invaders undergo peculiar changes and a certain kind of 

 leucocytes surround them with a wall. Sometimes a con- 

 nective tissue capsule forms around it all and then the 

 bacilli may become secluded, incarcerated so to speak, 

 and innocuous temporarily or forever. Frequently, how- 

 ever, the tubercle bacilli multiply and produce poisons 

 which kill the tissue around them; they spread in the 

 neighboring tissue; they soften the tissue locally through 

 killing it and may thus break into lymph and blood ves- 

 sels and are carried to distant parts where they set up 

 similar processes. They produce substances which are 

 toxic and which disturb the general condition of the in- 

 vaded organism, and the latter usually responds with the 

 production of antagonistic substances which counteract 

 to a certain extent the toxic substances of the bacteria 

 and thus may cause either a certain degree of immunity 

 against the bacillus and its products, or, on the contrary, 

 hypersusceptibility. Such immunity reactions on the 

 part of the host are quite common in bacterial infectious 



