Manchester Memoirs, Vol. xliii. (1899), No. \%. 7 



exhausted of free oxygen and are protected from fresh 

 supplies by the layer of carbonic acid formed above — the 

 hypothesis that Koch's tubercle bacillus is an originally 

 harmless saprophyte or digestive ferment which has 

 been converted into a destructive parasite by imprison- 

 ment in lungs inefficiently aerated, either in consequence 

 of hereditary weak breathing habits or other obvious 

 causes. The view is a more hopeful one than that 

 which indefinitely multiplies species by giving to every 

 pathogenic microbe a permanently specific character ; 

 for in the former case we may hope to escape disease 

 germs by sanitary conditions which prevent their evolu- 

 tion, while in the latter our escape is a mere matter of 

 good luck. 



Jt is Vv^ell-known that the cancerous growth after 

 removal by surgical operation, even to the extent of 

 amputation, will often re-appear in other parts of the body. 

 Now, it is authoritatively stated that the cells of such second 

 growths have always the characteristic form, not of the 

 epithelial cells of the locality of the second outbreak, but 

 of the region where the disease first appeared. Thus, let 

 us take two remote portions of the body, A and B. If 

 the disease first appears at A, then a re-appearance at 

 B will have the characteristic cell formation of the 

 epithelium at A ; if, on the other hand, it originates at B, 

 and re-appears at A, the growth at A will have the 

 characteristic cell formation, not of the epithelial cells of A, 

 but of those of B. The only explanation yet put forward 

 is that a morbid cell from the original growth has escaped 

 and been conveyed by the blood vessels or the lymphatics, 

 as a travelling cell, to find a lodgment where it can parasiti- 

 cally develope a new colony. The characteristic form of the 

 cells of the morbid growths clearly indicates their descent 

 from the originally healthy cells of the epithelium where 



