Decembee 31. 1920] 



SCIENCE 



627 



(higli degree of specificity and the enduring 

 immunity whicli follows recovery from an at- 

 tack. This is true am.ong animals, for instance, 

 of hog cholera and foot and mouth disease, 

 and in man of poliomyelitis. This specificity 

 is shown by the difSculty or impossibility of 

 implanting the virus on specifically remote 

 animals. In poliomyelitis, for example, only 

 monkeys are subject to experimental infection, 

 in hog cholera and foot and mouth disease, 

 only sTvine and cattle. Bearing in mind Beh- 

 ring's dictum that to produce a therapeutic 

 serum, it is essential to immunize hig'hly sus- 

 ,ceptibie animals, it becomes evident why suc- 

 cess has not crowned the many undertakings 

 to prepare an antipoliomyelitis serum m the 

 horse or other large animal, and why it is only 

 by the use of swine themselves that an anti- 

 hog-cholera serum has been secured. 



The investigation of this class of excess- 

 ively minute or filterable parasites casts a 

 sharp ray of light into a neighboring field of 

 biological research which at the time aroused 

 hopes of fiirther rapid progress but which the 

 intervening time and effort have not realized. 



Perhaps no subject in experimental pathol- 

 ogy has been pursued with more thought and 

 energy than the one to which the name of 

 cancer researdh is applied. The reasons are 

 obvious. The nature of the source of the can- 

 cerous tumors is still shrouded in essential 

 darkness. It is, of course, known that cancer 

 sometimes follows upon prolonged irritation 

 and inflammation of tissues variously excited. 

 But what the immediate impulse is that calls 

 forth the cancerous state is unknown. And 

 yet advances have come from the study of the 

 spontaneous and transplantable cancers in 

 mice, rats and some other animals. A long 

 ^eries of biological conditions governing the 

 growth and recession of the tumors have been 

 uncovered, and by altering those conditions, on 

 the one hand growth can be promoted, and on 

 |the other, retarded. In this way. Murphy and 

 )iis coworkers have accounted for the influence 

 of the action of the X-ray in affecting cancer 

 growth; and by observing the correlative ef- 

 fects on the lymphoid structures of the body, 

 ,which are very sensitive to the rays, and the 



.changes corresponding to them in the circu- 

 lating blood, they have so altered the scale as 

 almost at will eiither to aibolish or stiumlate the 

 .development of mouse cancers. 

 . But these experimental results and others of 

 a class in whidh the defensive forces of the 

 .body can be marshalled against the implanted 

 .cancer cells, throw no real light upon the 

 series of events underlying the origin of can- 

 cer. The light referred to was shed by the 

 studies of Rous, of the Rockefeller Institute, 

 upon a sarcoma, or fleshy cancer, of the do- 

 mestic fowl. This cancer, which arises at times 

 spontaneously in fowl, is subject to successful 

 implantation in other fowl. The specificity is 

 accurate; it will not grow in other birds and 

 grows best in the variety of fowl in an indi- 

 vidual of which it originally appeared. Its 

 igrowth is first local, as is cancer in man, and 

 later metastatic, or, appearing at a distance 

 and starting from microscopic masses of cells 

 ,derived from the original tumor and carried 

 by the circulation to remote parts of the body. 

 The altogether new and unprecedented fact 

 jabout this tumor, which has, however, not yet 

 been found to be true of the cancers of mam- 

 mals, is that it may be induced by the injec- 

 tion into the susceptible variety of fowls, of a 

 iCell-free filtered extract ol the tumor. In 

 .other words, Rous has accomplished for this 

 tumor what bacteriologists had effected for a 

 certain refractory group of the infectious and 

 communicable diseases, namely, relating it to 

 a form of life not imagined by the founders of 

 bacteriology, but which their discoveries in the 

 field of the living microscopic, as opposed to 

 the ultramicroscopic, imiverse brought within, 

 •range of recent biological research. 



SPmOCHETES 



The vicissitudes of bacteriological science, 

 like those of other sciences, have depended 

 upon time and method, and sometimes the 

 one and sometimes the other has served to 

 promote discovery. When by a happy con- 

 junction of circumstances, time and method 

 happen to conjoin, then advances almost start- 

 ling in nature may take place. 



It is in this way that we may view the re- 



