THE COMMON 'COLD 437 



percentages of pneumococcus, streptococcus carriers, a fraction of 

 a per cent of virulent diphtheria carriers, and that in this group a 

 number of the carriers begin to cough, spit and hawk, the percentage 

 of all these will go up, and susceptible contacts will not only contract 

 the cold, but will get the specific disease. These facts have been 

 noted in the case of meningococci by Bassett-Smith, 1 for diphtheria 

 bacilli by Moss, 2 and the writer has frequently noted this with pneu- 

 mococci and streptococci in army camps. 



It is thus seen that the common cold offers indirect problems of 

 great importance, and that the fluctuations of the bacterial flora of 

 the mouth, nose and throat, incident to the common colds, are of 

 interest entirely apart from the problems of specific etiology of the 

 cold itself. 



As to the etiology of so-called colds, little is definitely known. It 

 is uncertain whether it is caused by a single or by a variety of 

 infectious agents. Though streptococci, pneumococci, and numerous 

 other organisms have been described as possible causative agents, to 

 none of these can etiological importance be conclusively attached. 

 Kruse 3 in 1914 published work which suggests that the cold may 

 be due to a filterable virus. He succeeded in transmitting the condi- 

 tion to human beings with filtered mucus. Similar work by Foster 4 

 in 1917 has seemed to bear out Kruse 's contention. Foster went so 

 far as to believe that he had cultivated the filterable virus by the 

 anaerobic methods utilized by Noguchi and others in treponema 

 cultivation, and described in another place. An experiment done by 

 Hopkins in our laboratory suggests similarly the participation of a 

 filterable virus, but it must be remembered that experiments during 

 the season of colds on human beings are fraught with many possi- 

 bilities of error, and many recent workers have failed to obtain 

 positive results. The etiology of the common cold, therefore, is in 

 doubt, and awaits further elucidation. 



Meanwhile, the sanitary importance of the condition must not be 

 underestimated, and the principles of prevention are prefectly plain, 

 although they offer almost insuperable difficulties to successful 

 enforcement. 



1 Bassett-Smith, Lancet, 194, 1918, 290. 



-Moss, Guthrie and Gelicn, Transac. 1511) Internal.. Congress, Hygiene, Wash- 

 ington, 1913. < 



3 Kruse, Munch. Med. Woch., 61, 1914, 1547. 



4 Foster, Jour. Infec. Dis., 21, 1917, 451. 





