66 The Science of Life. 



are known". This was partly based on Schwann's 

 researches on fermentation and putrefaction, and on 

 Bassett Audouin's proof that the muscardin disease of 

 silkworms was due to a contagium mvum. 



The classic monument of this fourth level of analysis 

 is, however, Virchow's Cellular Pathology (1858), in 

 which he showed that disease may often be localized in 

 cell-systems and cell-territories, and sought to express 

 both morbid growths and morbid stages in terms of 

 abnormal cell-multiplication and reaction. "Nothing", 

 Prof. Greenfield says, "could have been further from 

 the central idea of Virchow's teaching than the mere 

 mechanical application of cellular structure to the eluci- 

 dation of the phenomena of life and of disease. It is 

 the living cell, endowed with vitality and with function, 

 governed by laws of existence, capable of self-multiplica- 

 tion and propagation, and arranged in organic systems, 

 which he studies. It is the cell as the living active agent 

 in the production of disease, and the arrest or perversion 

 of its action by disease-producing causes, which have 

 the highest place in his thoughts." The author of the 

 famous dictum, omnis cellula a cellula, has said of his 

 own work, " I blocked for ever the last loophole of the 

 opponents, the doctrine of specific pathological cells, by 

 showing that even diseased life produced no cells for 

 which types and ancestors were not forthcoming in 

 normal life". 



As with physiology, so here, there is still work being 

 done, and much to be done, at the four different levels of 

 interpretation which represent historical stages. We 

 have still to do with the pathology of the entire organ- 

 ism with the problem of attaching definite meaning to 

 such phrases as "constitution", "congenital tendency", 

 "diathesis", and the like. And it is not easy to avoid 

 verbalism on the one hand, and a violation of the unity 

 of the organism on the other. We have still to do 

 with the pathology of organs, which has hardly passed 

 beyond man and the more important domestic animals. 

 Roux's suggestive conception of "the struggle of parts 

 within the organism" remains but little worked, and 

 the relations of disease-variations to those which form 



