Decembee 31, 1920] 



SCIENCE 



625 



|Wliether exposed children do or do not carry 

 jini their blood, spontaneously as one might 

 (Say, sufficient diphtheria antitoxin to afFord 

 them security without a protective serum in- 

 jection. And beside the benefits accruing to 

 human therapy directly from the working out 

 of the meaning of anaphylaxis are to be placed 

 those improvements introduced into veterinary 

 practise, from which human preventive medi- 

 cine also has derived great gain, namely, 

 the application of the tuberculin test in clear- 

 ing milch herds of actively tubercular cattle, 

 ,and of mallein to the controlling of glanders 

 .among horses. 



FILTERABLES 



As we move from the contemplation of one 

 achievement to another in bacteriology, we 

 .rarely pause to reflect how far circumstances 

 almost accidental have favored the gains. The 

 working out of the biological basis of fermen- 

 tation and putrefaction, and a little later of 

 the microbic origin of disease, is obviously 

 bound up with the perfection of the compound 

 microscope, and the usefulness of that instru- 

 ment for the purpose is as obviously bound up 

 with the ultimate size of bacteria and related 

 organisms. And yet without the fortunate con- 

 junction of an optical device and the degree of 

 magnitude of living objects, we should still be 

 groping in outer darkness in the search for 

 the origin of disease, and still struggling with 

 the phantoms of spontaneous generation. But 

 the great men who proved the connection be- 

 tween microscopic life and the biological 

 processes mentioned, including the source of 

 the infectious diseases, did more than describe 

 the phenomena revealed by the microscope and 

 ptherwise. They established methods with 

 principles so clearly enunciated and rigidly 

 based that it has been found possible to pene- 

 jtrate into an inhabited territory in which thus 

 ^ar the most powerful microscope has not al- 

 iWays enabled us to discern the living forms. 

 , Thanks to their labors we know now, first, 

 that the faculty of setting up disease in stic- 

 cessive individuals is a property only of mat- 

 ;ter which can itself increase indefinitely, and 

 all matter thus constituted is possessed of life; 

 and second, that certain disease producing 



parasites can be separated mechanically from 

 the soluble products of their growth, by pas- 

 sage through earthenware filters, in which the 

 interstices or pores are smaller even than the 

 size of the microbes themselves. By varying 

 the density or porosity of these filters, we ar- 

 rive at a way of roughly estimating the size of 

 the microbic cells. 



I Thus it came about that in 1898 two Ger- 

 man bacteriologists, Loeffler and Frosch, who 

 were engaged on the study of the very highly 

 communicable foot and mouth disease of cattle, 

 discovered that after diluting the contents of 

 the unbroken vesicles which arise in that dis- 

 ^ease, with 20 to 40 times their volume of 

 water and passing them through such earthen- 

 ware filters, the filtrate not only would induce 

 the disease on inoculation, but that the same 

 series of events followed the dilution and 

 inoculation of the vesicular contents of the 

 experimental variety of disease through an 

 indefinite series. Obviously the filtrate con- 

 tained a living element which came to be 

 called a virus, just as is the smallpox germ, 

 for in neither instance, and notwithstanding 

 laborious endeavors, has the living organism 

 itself ever been seen under the microscope. 



We now recognize a class of microbes or 

 /viruses which are so minute as to be regarded 

 ,as ultramicroscopic, and yet so active as to be 

 capable of setting up disease in animals and 

 man. The precise limits of the class have yet 

 jto be defined. When we consider that there 

 iremain still to be detected the microbic inci- 

 tants of some of the most contagious as well as 

 common of diseases, our minds readily seize 

 hold of the possibility of their being of this 

 nature. Thus the microbes responsible for 

 3uch contagious maladies as measles, scarlet 

 fever, and chicken pox, and those inducing 

 smallpox and rabies are not known, and not 

 a little obscurity still surrounds the etiology, 

 as we say, or immediate origin of epidemic in- 

 fluenza. 



, Inasmuch as the fllterable microorganisms 

 or viruses, or filter passers as the British pre- 

 jfer to call them, are known alone through 

 their disease-producing propensities, no one 

 can say whether, as is true of the bacteria, in- 



