522 HILDA HEMPL HELLER 



All strains were carefully isolated and the cultures were con- 

 tinually observed in order to detect contaminations. ^ 



The samples collected, though they do not exhaust the patho- 

 logical material from anaerobic infections, are very widely repre- 

 sentative, and the collection of much more material and the 

 isolation from it of many more pathogenic strains would be an 

 exceedingly arduous task. It must also be borne in mind that 

 in greatly increasing the number of strains under observation 

 one must necessarily relax the vigilance with which he criticises 

 the purity of those strains which are studied. The examination 

 of any considerable number of anaerobes is a comparatively 

 new task, and any proposal for classification which is made 

 at the present period is bound to be a temporary one. The 

 time is unquestionably not ripe for an elaborate study of several 

 hundred strains of any particular type of anaerobe because the 

 material for such a study has never been collected, and such a 

 collection would represent several years' work and a consider- 

 able outlay for experimental animals. But the cultures that I 

 have been able to isolate during the past few years have furnished 

 so much material for investigation, and the information gained 

 from them has so radically altered my attitude toward the 

 anaerobic group, that I feel that the time has arrived to state 

 my results, to organize them as consistently as may be, and to 

 propose a system for their classification. In other words I feel 

 that the status of the classification of the anaerobes is today so 

 chaotic and unsatisfactory that a pioneer effort at a logical 

 grouping according to our present knowledge is very much 

 needed. If we consider the fact that the investigated material, 

 when compared with the vast amount of uninvestigated material, 

 is exceedingly scanty, we shall not expect such a classification 

 to be final. We have today, however, a fairly definite con- 

 ception of the pathogenic anaerobes, and by analyzing the 



2 An account of the affinities of the animal strains studied will be found in 

 part in The Journal of Infectious Diseases for November, 1920, Vol. 27, and in 

 full in the Collected Reprints of the Hooper Foundation for 1921, Vol. VI, under 

 the title "Etiology of Acute Gangrenous Infections of Animals." This paper 

 contains a description of the methods employed in the isolation of my cultures. 



