DISEASES PREVALENT IN THE ARMY 303 



in their study during recent years than in the diseases of the 

 digestive tract, or in the tropical diseases or in several other 

 categories of diseases. The reason for this is not perfectly 

 plain, but it is perhaps because all these are diseases of human 

 beings alone, having nothing in common with the diseases of 

 animals or with those carried by insects or other hosts, and 

 for this reason are not easily made the subject of experimental 

 research on laboratory animals. In addition, the respiratory 

 diseases are the most common of all human ailments, and most 

 of them are so trivial that they have not received the study and 

 attention that have been given to more fatal maladies. Very 

 few of us give much consideration to a common cold and yet 

 in the mystery of the common cold may lie the secret of many 

 of the acute infections of the respiratory system. 



At the beginning of the war there was every reason for 

 expecting a considerable number of cases and deaths from pneu- 

 monias, since that had been the experience of the Civil War, 

 and in civil life the percentage of deaths due to lobar pneumonia 

 has been relatively increasing during recent decades as the more 

 easily preventable diseases decreased. An orderly understand- 

 ing of acute lobar pneumonia had also been arrived at through 

 the work of Rufus Cole, Avary, Dochez, Chickering, and 

 others at the Rockefeller Hospital, New York. The work 

 began some years ago, about 1913, in fact, but the subject was 

 complicated and difficult and progress, although steady, was 

 slow. In the end, however, these investigators showed that 

 the organisms which cause lobar pneumonia may be grouped 

 into four classes, which they have designated as types one, 

 two, three and four. The first three of the types are fixed 

 and are readily identified by agglutination and precipitin tests 

 and by some other biological and cultural tests. The fourth 

 type, however, is made up of the irregular organisms which 

 do not fall into any one of the first three types. The fixed 

 types are clear cut homogeneous groups made up of similar 

 individuals, while the fourth type consists of a large number of 

 irregular organisms which bear no relation to the other groups, 



